The fungal GATA factors

126 The fungal GATA factors Claudio Scazzocchio The DNA-binding domains of eucaryotic GATA factors comprise a four-cysteine Zn finger and an adjacent basic region. Fungal GATA factors regulate nitrogen metabolism, light induction, siderophore biosynthesis and mating-type switching. Hydrophobic interactions determine binding-site specificity. Interactions with other factors may determine promoter specificity. One GATA factor has recently been shown to determine a drastic chromatin rearrangement. Addresses Institut de Génétique et Microbiologie, CNRS UMR 8621, Université Paris-Sud, Bâtiment 409, Centre d’Orsay, 91405 Orsay cedex, France; e-mail: [email protected] Current Opinion in Microbiology 2000, 3:126–131 1369-5274/00/$ — see front matter © 2000 Elsevier Science Ltd. All rights reserved. domains has been published [8•] and a comparison of different domains is shown in Figure 1. DNA binding High-resolution NMR structures exist for two GATAbinding domains: the chicken GATA-1 carboxy-terminal domain and the Aspergillus nidulans AreA single domain [9,10••]. The domain is a compact structure formed by two pairs of β-sheets followed by an α-helix and a non-structured tail (Figure 2). Side chains of the Zn core module make largely hydrophobic contacts in the major groove of the DNA and the carboxy-terminal tail contacts the phosphate backbone. The carboxy-terminal domain of the chicken GATA-1 lies in the minor groove, whereas the corresponding sequence in the A. nidulans AreA runs at the edge of the minor groove, parallel to the phosphate backbone ([10••]; see Figure 3). Introduction: definition and phylogeny GATA factors are a class of transcriptional regulators present in fungi, metazoans and plants. A DNA-binding domain that recognises a six base-pair sequence with a GATA core defines a GATA factor. The consensus recognition sequence is HGATAR [1–3]. The DNA-binding domain comprises a four-cysteine Zn finger followed by a basic terminal domain. In vertebrates, two domains separated by a few amino acids are present with the carboxy-terminal domain being the physiological DNAbinding domain. The amino-terminal domain may modulate binding specificity and/or participate in interactions with other proteins [4,5]. The metazoan GATA Zn fingers always have a 17-residue loop and a leucine (an alanine in some Caenorhabditis elegans fingers) in the seventh position of the Zn finger loop. In invertebrates both two-domain and one-domain factors are found. Plant GATA factors have one binding domain and 18 residues in the Zn finger loop, the additional residue being a lysine in position 16. Plant databases reveal putative GATA factors with either leucine or glutamine in the seventh position of the loop. Fungal GATA factors come in two kinds: one is ‘animal-like’ and the second is ‘plantlike’. The residue at position seven of plant-like fungal GATA factors is glutamic acid [6]. In the genome of Saccharomyces cerevisiae, I find eight proteins with GATAbinding domains: four are ‘animal-like’, a fifth is similar to the ‘plant-like’ domains of other fungi, while three others, clearly ‘GATA factors’, show departures from the consensus. With one exception, fungal GATA factors contain only one DNA-binding domain. It is possible that GATA DNA-binding domains are a very ancient eukaryotic motif. A motif obviously related to GATA factors is found in the stalky gene of Dictyostelium discoideum [7]. We do not know if GATA factors are present in other early eucaryotic branches. A dendogram of GATA-binding The function of GATA factors — general considerations In vertebrates, GATA factors participate together with other transcription factors in terminal differentiation. There are six GATA factors in mammals. The first discovered and best known, GATA-1, is essential for the differentiation of the erythroid and megaloblastoid cell lines [11]. Others participate in the differentiation of T cells, the endothelium of the gut, and in heart differentiation [12•,13,14]. End-1 and Elt-1 are involved in the differentiation of the endoderm in C. elegans [15]. In Drosophila GATA factors regulate immune response, bristle pattern and yolk protein synthesis [16–18]. Little is known of the function of GATA factors in plants. Although light-inducible promoters contain functionally significant GATA boxes, no involvement of a specific GATA factor has being demonstrated. An interesting case is the promoter of the nitrite reductase gene of Arabidopsis thaliana. This gene is induced both by light and nitrate. By analogy to fungi (see below), GATA sites were sought and found by in vivo footprinting in the nitrite reductase gene promoter [19]. To date, however, no GATA factor has been found to act as a specific regulator of nitrogen assimilation pathways in plants. There are a limited number of GATA factors in sequenced genomes, including metazoa genomes. This contrasts with the abundance of transcription factors such as the classic Zn fingers. There is no functional conservation across the fungal and metazoan kingdoms or between vertebrates and invertebrates (with the possible exception of endothelial differentiation [15]). The structured motif and DNA binding specificity are conserved, but the rest of the protein is not. The same motif and binding specificity serve different The fungal GATA factors Scazzocchio 127 Figure 1 Varieties of GATA DNA-binding domains in eucaryotes. A.t. GATA-3, a factor of unknown function from Arabidopsis thaliana; StkA (Stalky), a factor involved in spore maturation in Dictyostelium discoideum; WC1, a ‘plantlike’ GATA factor involved in photoinduction in N. crassa; ASH1 an aberrant GATA-binding domain of S. cerevisiae, involved in the determination of mother–daughter cell asymmetry; AreA, a typical ‘animal-like’ fungal GATA-binding domain (see text for more details); cGATA-1 (N) and (C), amino- and carboxy-terminal GATA-binding domains of the chicken GATA-1 factor (note that the last four residues of the amino-terminal domain are down again as the first four residues of the carboxy-terminal domain); elt-1, a GATA factor from C. elegans (see text); Serpent, a onefinger GATA factor from D. melanogaster involved in regulating resistance to pathogens. The sequence of AreA corresponds to that in Figure 2 and the lengths of the other sequences included were selected so as to purposes in different contexts. Below I describe the functions of GATA factors in fungi. Canonical ‘animal’ 1–finger GATA factors: general regulation of nitrogen metabolism in the ascomycetes match this sequence. Amino acid residues in red indicate universally conserved residues, and those in green indicate residues conserved in a majority of the factors shown in this figure. Note that AreA belongs clearly to the ‘animal’ class of GATA domains. GATA factor. The binding (or activation) of the specific factor is thought to demand the presence of the specific inducer; that of the broad-specificity GATA factor, a low Figure 3 In the ascomycetes the utilisation of nitrogen sources is subject to two levels of transcriptional control, specific induction and nitrogen metabolite repression [20]. For example, to induce nitrate and nitrite reductases both the presence of nitrate and the absence of ammonium and glutamine are needed [21••]. The transcription of genes involved in the utilisation of most nitrogen sources requires two transcription factors (Figure 4). Each pathway is regulated specifically by a transcription factor of the Zn binuclear cluster class. The general regulator is always a Figure 2 The sequence (left) and ribbon representation (right) of the DNAbinding domain of the fungal GATA factor AreA. Amino acid residues in red indicate those that participate in β-sheet formation, those in blue indicate residues that participate in helical structures and those in black indicate residues that participate in non-structured regions. In the ribbon representation these are indicated respectively in red, blue and white. The leucine in the seventh position of the loop, discussed in the text, is marked with an asterisk. Modified with permission from [10••]. Comparative view of the chicken GATA-1 and AreA complexes with DNA. AreA backbone, red ribbon; GATA-1 (carboxy-terminal DNA binding domain) backbone, green ribbon. The pink colour represents a difference between the two proteins in the φ/ψ backbone angles, which results in a different orientation of the backbone in relation to the minor groove. The residue at this position is glycine in GATA-1 and valine in AreA. Note that the non-structured carboxyl terminus of AreA is parallel to the phosphate backbone, while for GATA-1 it lies within the minor groove. The long helical sequence (in blue in Figure 2), for both proteins, lies in the major groove, almost perpendicular to the plane of the paper. A number of side chains participating in DNA binding are shown: in AreA side chains are yellow, and in chicken GATA-1 side chains are blue. The major groove is blue, and minor groove is orange. Modified from [10••] with permission. 128 Cell regulation Figure 4 Schematic representation of the 1200 bp niiA (nitrite reductase) niaD (nitrate reductase) intergenic region of Aspergillus nidulans. This region is a genuine bidirectional promoter. The circles represent positioned nucleosomes. Both AreA and NirA binding is essential for transcriptional activation. Ten AreA (GATA) binding sites are present. Four of these are in intracellular concentration of (presumably) glutamine. The process is very well understood and very similar in Aspergillus nidulans and Neurospora crassa [22]. The master gene and GATA factor of nitrogen regulation is NIT2 in N. crassa and areA in A. nidulans [20]. The accepted model is that a negative-acting protein, NMR, complexes with NIT2 (and AreA) in the presence of repressing nitrogen sources. The real effector may be glutamine. NMR interacts both with residues in the DNA-binding domain and in the carboxyl terminus of AreA and NIT2. It has been then proposed that NMR prevents NIT2 and AreA binding to DNA [23,24]. At least for AreA, there are two other levels of regulation: first, transcription of areA is autoregulated and second, the stability of the areA mRNA is lower in mycelia grown on repressing nitrogen sources [24]. The relative importance of these mechanisms does not seem identical in the two organisms, NMR-mediated repression seems crucial in N. crassa and less so in A. nidulans [25]. Although it is clear that AreA and NIT2 binding is necessary for expression of the scores of genes involved in the utilisation of nitrogen sources, it is not clear whether they directly activate transcription or assist in the recruitment of the factors specific for each pathway. For some promoters it is clear that the specific factor and AreA do not act additively: they are both essential to elicit transcription above the basal level [21••,26]. In S. cerevisiae the basic pattern of regulation is the same but there are four GATA factors involved, which are interconnected in a complex regulatory network: Gln3p and Gat1p are transcriptional activators, while Dal80p and GFZ3 are repressors [27,28,29•]. There exists in A. nidulans a homologue of DAL80, the areB gene. This gene was first defined by suppressors of null areA– mutations. These suppressors are chromosomal aberrations [30] that probably add an activation domain to AreB. Loss-of-function mutations indicate that AreB has, just as Dal80p and Gfz3p, a repressive, albeit a nucleosome-free sequence and they contribute to more then 80% of the transcriptional activity for both niiA and niaD. The binding sites 2 and 3 (from left to right) for the pathway-specific transcription factor NirA act bidirectionally, play an essential role in transcriptional activation and are placed at the edge of positioned nucleosomes. Only binding by AreA is necessary for chromatin rearrangement. A nucleosome whose displacement could not be determined with the techniques used is shown in light grey. Non-expression conditions are in the absence of inducer (nitrate) and/or the presence of repressor (ammonium). Expression conditions necessitate the presence of nitrate and the absence of ammonium (see [21••] and references therein). less crucial, role (CH Zadra, H Haas, M Jones, HN Arst Jr and MX Caddick, personal communication). It is interesting to compare the classic simplicity of nitrogen source regulation in A. nidulans and N. crassa with the baroque complexity of regulation in S. cerevisiae. The ecology of the organisms is rather different; the two filamentous fungi are rather ‘wild’ and represent probably the general situation in the ascomycetes, whereas baker’s yeast is a very domesticated organism. The haploid genome of S. cerevisiae is most likely to be derived from an ancestral diploid and thus there have been two sets of genes able to diverge in the course of the evolution of the organism. A similar situation is extant in carbon catabolite repression in which there is one master gene in A. nidulans, creA, [31] whereas there are two homologues, MIG1 and MIG2, in S. cerevisiae [32]. Canonical ‘vertebrate-like’ repressors with two fingers: regulation of siderophore biosynthesis Mutants of the basidiomycete Ustilago maydis derepressed for siderophore biosynthesis map in the urbs-1 gene. This gene encodes a GATA factor with two typical GATADNA-binding domains. Unlike in vertebrates where the DNA-binding motif of GATA factors are separated by only a few residues, the two motifs of urbs-1 are separated by 92 amino acid residues [33]. It has been demonstrated that, as in the vertebrate factors, the DNA-binding finger is the carboxy-terminal domain [34,35]. Regulators with similar sequences and functions have since been found in N. crassa, A. nidulans and P. chrysogenum [36•] (but not in the genome of S. cerevisiae) implying a conservation of siderophore biosynthesis control. Interacting ‘plant-like’ GATA factors: light regulation in N. crassa Many functions in N. crassa are inducible by blue light, including conidiation, mycelial carotenoid biosynthesis and resetting of the circadian rhythm. ‘Blind’ mutations The fungal GATA factors Scazzocchio map at only two loci, WC1 and WC2. These two loci encode ‘plant-like’ GATA factors [6,37]. These two factors act as a dimer and show typical PAS dimerisation domains. Where is the photoreceptor? It may well be WC1 itself. This protein (but not WC2) has a LOV domain, which has been shown in other systems to bind flavin-adenine mononucleotide, a suitable blue light receptor. WC1 is itself light-inducible, and this is dependent on both WC1 and WC2; however, the same is not true for WC2 — i.e. its photoinduction is not dependent on the WC1/WC2 complex [38]. WC1 when complexed with WC2 is phosphorylated in the presence of light. This leads to degradation of WC1. Thus a rapid light-induced turnover of WC1 in the WC1/WC2 complex is correlated with the induction of light-inducible promoters [39••]. The causal relationship between these two events remains to be determined. WC homologues exist in A. nidulans and P. chrysogenum; however, their function is unknown (H Haas, personal communication). A non-canonical factor involved in mating-type switching Ash1p of budding yeast has several unique features in its finger loop, it is nevertheless a GATA factor. Deletion of the gene results in massive daughter mating-type switching, whereas overexpression prevents mother switching. It represses the expression of the HO endonuclease in daughter cells, thus preventing daughter switching. ASH1 mRNA is specifically localised in the growing tips of daughter cells in association with a myosin molecule [40,41,42••]. Leucine in position 7, a paradigm in the investigation of detailed DNA–protein interactions HN Arst and collaborators have isolated scores of mutations in the AreA DNA-binding domain. As these mutations usually affect the growth of A. nidulans on all or some nitrogen sources, second site revertants can be isolated. These usually grow on some nitrogen sources but not on others, allowing the selection of second generation revertants, and so on. Thus, the AreA DNA-binding domain is a treasure trove of mutations, which coupled with structural or modelling studies provides an unequalled opportunity to study, both in vivo and in vitro, all possible binding patterns [24,43,44••]. I describe below one such example of the above. The leucine in the seventh position of the Zn finger loop is conserved in almost all ‘animal-like’ GATA factors (Figure 1). An areA102 mutant grows exceptionally well on some amides but not at all on uric acid. The mutation responsible is an Leu to Val change in position 7 of the loop. Revertants with a Val to Met change have ‘mirror image’ mutant phenotype (i.e. better growth on uric acid and worse growth on amides) [43]. Specific suppressors map to the promoters of the uric acid permease genes. A number of these are mutations of CGATAR or AGATAR to TGATAR. All sites in the promoter involved in utilisation 129 of amides are TGATAR sites [3]. The seventh positioned Leu makes a hydrophobic contact with the first base, whether that be A, C, or T. The shorter Val is within a van der Waals binding distance only to the bulky methyl of the T, whereas the longer Met contacts well A and C, but steric constraints prevent its contact with a T [3,45••]. Thus those C. elegans fingers and STALKY (see above) that have an Ala and a Thr, respectively, in this position should only recognise TGATAR sequences [3]. Ash1p has, uniquely, a cysteine in this position. It may be interesting to predict its binding specificity. The GATA domain, more to it than DNA binding A vexing problem is how, given the similarity of GATA DNA-binding domains, promoter specificity is achieved. Both in the mammalian and the fungal GATAs it has been established that the ‘GATA domain’ is able to interact with other proteins, including other Zn fingers [46••]. The domain of AreA/NIT2 can interact with an identical domain of a second molecule, the NMR protein and the specific regulator NirA/NIT4 ([3,23,47••]; MI Muro-Pastor and C Scazzocchio, unpublished data). It is still an open question whether AreA/NIT2 can also interact with other specific regulators and whether the common determinant of specificity is the presence in promoters of both AreA/ NIT2 and specific binding sites in close proximity [3]. GATA factors and chromatin rearrangements In both chicken and human β-globin gene cluster enhancers, it has been shown that GATA-1 is essential for the maintenance of DNase I hypersensitive sites [48,49]. GATA-1 is able to destabilise nucleosomes in vitro [50••]. The niiA–niaD (nitrite and nitrate reductase) bidirectional promoter of A. nidulans contains six positioned nucleosomes. In the presence of nitrate and the absence of ammonium, these nucleosomes vanish (Figure 4). The process is independent of transcription and of the presence of the NirA-specific factor, and is absolutely dependent on AreA [22]. A specific mutation in the AreA-binding domain results in constitutive chromatin rearrangement. The mechanism involved is at present unknown, but a possible lead is that the vertebrate GATA-1 DNA-binding domain is itself acetylated and thus may influence directly or indirectly histone acetylation [51•,52•]. Conclusions GATA factors are widespread eukaryotic regulators. In fungi they act as transcription factors or repressors in a number of different processes, ranging from nitrogen source utilisation to mating-type switching. The DNAbinding domains are rather special in that most of the specific interactions with nucleobases are hydrophobic. Mutational studies, coupled with the powerful selection techniques possible in fungi, provide a paradigm for the study of this type of side chain-nucleobase interactions, of the interactions with other proteins and of the role of transcription factors in chromatin remodelling. 130 Cell regulation The future research involving GATA factors will probably take two directions; the detailed study interactions of GATA factors with other transcription factors or regulators and their role in chromatin rearrangements in both fungi and mammals. It will be important to establish whether the latter arises directly from strains induced directly by DNA binding and/or whether GATA factors or complexes of GATA and other factors can recruit protein complexes known to destabilise chromatin. The role of acetylation of the GATA factors themselves and its possible relation with histone acetylation remains a completely open problem. Update While this review was being processed we obtained mutational evidence for the direct role of the GATA factor AreA in the chromatin rearrangement of the niiA–niaD promoter (MI Muro Pastor, A Ramón and C Scazzocchio, unpublished data). AreA acts also as a transcriptional co-activator of the prnD–prnB (proline oxidase-proline transporter) bidirectional promoter of A. nidulans. Drastic chromatin rearrangements also occur in this promoter, a situation that may seem completely analogous to the one described for niiA–niaD. Surprisingly these chromatin changes are totally independent from AreA, while they seem dependent on the specific activator of the above genes, PrnA (I García, R Gonzalez, D Gómez and C Scazzocchio, unpublished data). It is likely that the interplay of GATA and other factors be substantially different from one promoter to the other. Acknowledgements I am grateful to HN Arst Jr, MX Caddick, H Haas, SA Leong and G Macino for unpublished results and/or suggestions on the manuscript, A Gronenborn and colleagues for permission to use figures modified from [10••], and to J Valdez and I García and for help in the production of the figures and proof-reading of the typescript. References and recommended reading Papers of particular interest, published within the annual period of review, have been highlighted as: • of special interest •• of outstanding interest 1. Merika M, Orkin SH: DNA-binding specificity of GATA family transcription factors. Mol Cell Biol 1993, 13:3999-4010. 2. Ko LJ, Engel JD: DNA-binding specificities of the GATA transcription factor family. Mol Cell Biol 1993, 13:4011-4022. 3. Ravagnani A, Gorfinkiel L, Langdon T, Diallinas G, Adjaji E, Demais S, Gorton D, Arst HN Jr, Scazzocchio C: Subtle hydrophobic interactions between the seventh residue of the zinc finger loop and the first base of an HGATAR sequence determine promoterspecific recognition by the Aspergillus nidulans GATA factor AreA. EMBO J 1997, 16:3974-3986. 4. Yang HY, Todd E: Distinct roles for the two cGATA-1 finger domains. Mol Cell Biol 1992, 12:4562-4570. 5. Fox AH, Kowalski K, King GF, Mackay JP, Crossley M: Key residues characteristic of GATA N-fingers are recognized by FOG. J Biol Chem 1998, 273:33595-33603. 6. Ballario P, Vittorioso P, Magrelli A, Talora C, Cabibbo A, Macino G: White collar-1, a central regulator of blue light responses in Neurospora, is a zinc finger protein. EMBO J 1996, 15:1650-1657. 7. Chang WT, Newell PC, Gross JD: Identification of the cell fate gene stalky in Dictyostelium. Cell 1996, 87:471-481. 8. • Teackle GR, Gilmartin PM: Two forms of type IV zinc-finger motif and their kingdom-specific distribution between the flora, fauna and fungi. Trends Biochem Sci 1998, 23:100-102. The natural history and evolutionary relationship of GATA-binding motifs are described in this review. 9. Omichinski JG, Clore GM, Schaad O, Felsenfeld G, Trainor C, Appella E, Stahl SJ, Gronenborn AM: NMR structure of a specific DNA complex of Zn-containing DNA binding domain of GATA-1. Science 1993, 261:438-446. 10. Starich MR, Wikström M, Arst HN Jr, Clore GM, Gronenborn AM: •• The solution structure of a fungal AREA protein-DNA complex: an alternative binding mode for the basic carboxyl tail of GATA factors. J Mol Biol 1998, 277:605-620. Gronenborn and co-workers [9] pushed NMR to the limits of its resolutions, and presented the structure of the chicken GATA1–DNA complex. Here the same group continues the story and presents the structure of the fungal AreA–DNA complex. 11. Orkin SH: GATA-Binding transcription factors in hematopoietic cells. Blood 1992, 80:575-581. 12. Tsai FY, Browne CP, Orkin SH: Knock-in mutation of transcription • factor GATA-3 into the GATA-1 locus: partial rescue of GATA-1 loss of function in erythroid cells. Dev Biol 1998, 15:218-227. A recent article by the group of one of the leaders in the field of mammalian GATA factors [1,11]. 13. Gao X, Sedgwick T, Shi YB, Evans T: Distinct functions are implicated for the GATA-4, -5 and -6 transcription factors in the regulation of intestine epithelial cell differentiation. Mol Cell Biol 1998, 18:2901-2911. 14. Charron F, Paradis P, Bronchain O, Nemer G, Nemer M: Co-operative interaction between GATA-4 and GATA-6 regulates myocardial gene expression. Mol Cell Biol 1999, 19:4355-4365. 15. Zhu J, Hill RJ, Heid PJ, Fukuyama M, Sugimoto A, Priess JR, Rothman JH: end-1 encodes an apparent GATA factor that specifies the endoderm precursor in Caenorhabditis elegans embryos. Genes Dev 1997, 11:2883-2896. 16. Petersen UM, Kadalayil L, Rehorn KP, Hoshizaki DK, Reuter R, Engstrom Y: Serpent regulates Drosophila immunity genes in the larval fat body through an essential GATA motif. EMBO J 1999, 18:4013-4022. 17. Lossky M, Wensink PC: Regulation of Drosophila yolk protein genes by an ovary-specific GATA factor. Mol Cell Biol 1995, 15:6943-6952. 18. Haenlin M, Cubadda Y, Blondeau F, Heitzler P, Lutz Y, Simpson P, Ramain P: Transcriptional activity of Pannier is regulated negatively by heterodimerization of the GATA DNA-binding domain with a cofactor encoded by the u-shaped gene of Drosophila. Genes Dev 1997, 11:3096-3108. 19 Rastogi R, Bate NJ, Sivasankar S, Rothstein SJ: Footprinting of the spinach nitrite reductase gene promoter reveals the preservation of nitrate regulatory elements between fungi and higher plants. Plant Mol Biol 1997, 34:465-476. 20. Arst HN Jr, Cove DJ: Nitrogen metabolite repression in Aspergilus nidulans. Mol Gen Genet 1973, 126:111-141. 21. Muro-Pastor MI, Strauss J, González R, Scazzocchio C: The GATA •• factor AreA is essential for chromatin remodelling in an eucaryotic bidirectional promoter. EMBO J 1999, 18:1584-1597. The authors summarise the control of the niiA–niaD (nitrite and nitrate reductase) bidirectional promoter and establish its nucleosome structure. They determine that drastic chromatin rearrangement found under expression conditions is independent of transcription and of the specific factor NirA, but is strictly dependent on the GATA factor AreA. 22. Marzluf GA: Genetic regulation of nitrogen metabolism in the fungi. Microbiol Mol Biol Rev 1997, 61:17-32. 23. Xiao X, Fu Y-H, Marzluf GA: The negative-acting NMR regulatory protein of Neurospora crassa binds to and inhibits the DNAbinding activity of the positive-acting nitrogen regulatory protein NIT2. Biochem 1995, 34:8861-8868. 24. Platt A, Langdon T, Arst HN Jr, Kirk D, Tollervey D, Mates Sanchez JM, Caddick MX: Nitrogen metabolite signalling involves the Cterminus and the GATA domain of the Aspergillus transcription factor AREA and the 3′′ untranslated region of its mRNA. EMBO J 1996, 15:2791-2801. 25. Andrianopoulos A, Kourambas S, Sharp JA, Davis MA, Hynes MJ: Characterization of the Aspergillus nidulans nmrA gene involved in nitrogen metabolite repression. J Bacteriol 1998, 180:1973-1977. The fungal GATA factors Scazzocchio 26. Amrani L, Cecchetto G, Scazzocchio C, Glatigny A: The hxB gene, necessary for the post-translational activation of purine hydroxylases in Aspergillus nidulans, is independently controlled by the purine utilization and the nicotinate utilization transcriptional activating systems. Mol Microbiol 1999, 31:1065-1073. 27. Soussi-Boudekou S, Vissers S, Urrestarazu A, Jauniaux J-C, André B: Gzf3p, a fourth GATA factor involved in nitrogen-regulated transcription in Saccharomyces cerevisiae. Mol Microbiol 1997, 23:1157-1168. 28. Coffman JA, Rai R, Loprete DM, Cunningham T, Svetlov V, Cooper TG: Cross regulation of four GATA factors that control nitrogen catabolic gene expression in Saccharomyces cerevisiae. J Bacteriol 1997, 179:3416-3429. 29. Svetlov VV, Cooper TG: The Saccharomyces cerevisiae GATA • factors Dal80p and Deh1p can form homo- and heterodimeric complexes. J Bacteriol 1998, 180:5682-5688. There are a plethora of articles on the interactions of the four yeast GATA factors involved in nitrogen metabolite repression, by this and other groups (B André and B Magasanik, see [27,28]), I have chosen somewhat arbitrarily this one as recommended reading. 30. Tollervey DW, Arst HN Jr: Domain-wide, locus-specific suppression of nitrogen metabolite repressed mutations in Aspergillus nidulans. Curr Genet 1982, 6:79-85. 31. Scazzocchio C, Gavrias V, Cubero B, Panozzo C, Mathieu M, Felenbok B: Carbon catabolite repression in Aspergillus nidulans, a review. Can J Botany 1995, 73:S160-S166. 32. Luftiyya LL, Johnston M: Two zinc-finger-containing repressors are responsible for glucose repression of SUC2 expression. Mol Cell Biol 1996, 16:4790-4797. 33. Voisard C, Wang J, McEvoy JL, Xu P, Leong SA: urbs1, a gene regulating siderophore biosynthesis in Ustilago maydis, encodes a protein similar to the erythroid transcription factor GATA-1. Mol Cell Biol 1993, 13:7091-7100. 34. An Z, Mei B, Yuan WM, Leong SA: The distal GATA sequences of the sid1 promoter of Ustilago maydis mediate iron repression of the siderophore production and interact directly with Urbs1, a GATA family transcription factor. EMBO J 1997, 16:1742-1750. 35. An Z, Zhao Q, McEvoy J, Yuan WM, Markley JL, Leong SA: The second finger of Urbs1 is required for iron-mediated repression of sid1 in Ustilago maydis. Proc Natl Acad Sci USA 1997, 94:5882-5887. 36. Haas H, Zadra I, Stoffler G, Angermayr K: The Aspergillus nidulans • GATA factor SREA is involved in regulation of siderophore biosynthesis and control of iron uptake. J Biol Chem 1999, 274:4613-4619. The work of Leong and co-workers [33–35] established that key regulator of siderophore biosynthesis in a basidiomycete is a two-fingered GATA factor. This article extends the work to a model ascomycete. 131 42. Munchow S, Sauter C, Jansen RP: Association of the class V •• myosin Myo4p with a localised messenger RNA in budding yeast depends on She proteins. J Cell Sci 1999, 112:1511-1518. Among a large number of excellent articles on ASH1 I have chosen these from three different groups for recommended reading [40,41,42••]. Together they describe the establishment of a factor involved in mother/daughter cell asymmetry, and the establishment of the mechanism of mRNA localisation by association with a myosin molecule. 43. Kudla B, Caddick MX, Langdon T, Martinez-Rossi NM, Bennett CF, Sibley S, Davies RW, Arst HN Jr: The regulatory gene areA mediating nitrogen metabolite repression in Aspergillus nidulans. Mutations affecting specific gene activation alter a loop residue of a putative zinc finger. EMBO J 1990, 9:1355-1364. 44. Wilson RA, Arst HN Jr : Mutational analysis of AREA, a •• transcriptional activator mediating nitrogen metabolite repression in Aspergillus nidulans and a member of the ‘streetwise’ GATA family of transcription factors. Microbiol Mol Biol Rev 1998, 62:586-596. The work of HN Arst Jr and then MX Caddick has been fundamental in our understanding of fungal (and other) GATA factors. [20,24,30,43]. The work by Arst Jr and Cove [20] is the foundation article of the field. This old, little known jewel of an article, should be obligatory reading. It establishes by classical genetics almost everything that is worth knowing about carbon and nitrogen metabolic repression in fungi. This latest review article [44••] is perhaps the most thorough mutational study ever of a DNA-binding domain. Perhaps, one day, structural and/or modelling studies will tell us why each mutant is a mutant and how second site revertants act. 45. Starich MR, Wikström M, Schumacher S, Arst HN Jr, Gronenborn AM, →Val mutant AREA •• Clore GM: The solution structure of the Leu22→ DNA binding domain complexed with a TGATAG core element defines a role for hydrophobic packing in the determination of specificity. J Mol Biol 1998, 277:621-634. Ravagnani et al. [3] proposed a model for specificity recognition, this work establishes the real structures underlying the specificity of the conserved leucine of the loop. 46. Mackay JP, Crossley M: Zinc fingers are sticking together. Trends •• Biochem Sci 1998, 23:1-4. A good review on the protein–protein interactions of Zn fingers, including GATA factors. 47. •• Feng B, Marzluf GA: Interaction between major nitrogen regulatory protein NIT2 and pathway-specific regulatory factor NIT4 is required for their synergistic activation of gene expression in Neurospora crassa. Mol Cell Biol 1998, 18:3983-3990. This, and [23] by the same group illustrate (in vitro) the potential for protein–protein interaction of the single NIT2 GATA-binding domain. Given the sequence identity, this work can be extended to AreA and other fungal homologous regulators, but probably not to those of S. cerevisiae. 48. Stamatoyannopoulos JA, Goodwin A, Joyce T, Lowrey CH: NF-E2 and GATA binding motifs are required for the formation of Dnase I hypersensitive site 4 of the human β-globin locus control region. EMBO J 1995, 14:106-116. 37. Linden H, Macino G: White collar 2, a partner in blue-light signal transduction, controlling expression of light-regulated genes in Neurospora crassa. EMBO J 1997, 16:98-109. 49. Boyes J, Felsenfeld G: Tissue-specific factors additively increase the probability of the all-or-none formation of a hypersensitive site. EMBO J 1996, 15:2496-2507. 38 Ballario P, Macino G: White collar proteins: PASsing the light signal in Neurospora crassa. Trends Microbiol 1997, 5:458-462. 50. Boyes J, Omichinski J, Clark D, Pikaart M, Felsenfeld G: Perturbation •• of nucleosome structure by the erythroid transcription factor GATA-1. J Mol Biol 1998, 279:529-544. This, together with [48,49], establishes the involvement of GATA1 in chromatin re-arrangements in mammalian promoters. 39 •• Talora C, Franchi L, Linden H, Ballario P, Macino G: Role of a white collar-1-white collar-2 complex in blue-light signal transduction. EMBO J 1999, 18:4961-4968. The authors demonstrate the phosphorylation and turnover of WC1 and propose specific roles for a WC1/WC2 heterodimer. 40. Sil A, Herskowitz I: Identification of asymmetrically localized determinant, Ash1p, required for lineage-specific transcription of the yeast HO gene. Cell 1996, 84:711-722. 41. Long RM, Singer RH, Meng X, Gonzalez I, Nasmyth K, Jansen RP: Mating type switching in yeast controlled by asymmetric localization of ASH1 mRNA. Science 1997, 277:383-387. 51. Boyes J, Byfield P, Nakatani Y, Ogryzko V: Regulation of activity of • the transcription factor GATA-1 by acetylation. Nature 1998, 396:594-598. See annotation [52•]. 52. Hung H-L, Lau J, Kim AY, Weiss MJ, Blobel GA: CREB-binding • protein acetylates hematopoietic transcription factor GATA-1 at functionally important sites. Mol Cell Biol 1999, 19:3496-3505. The first two papers [51•,52•] of a coming flood showing that GATA factors are acetylated and disagreeing on the effect of acetylation on DNA binding.