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Temperature-sensitive mutants are variants of genes that allow normal function of the organism at low temperatures, but altered function at higher temperatures. Cold sensitive mutants are variants of genes that allow normal function of the organism at higher temperatures, but altered function at low temperatures.
Mechanism
editMost temperature-sensitive mutations affect proteins, and cause loss of protein function at the non-permissive temperature. The permissive temperature is one at which the protein typically can fold properly, or remain properly folded. At higher temperatures, the protein is unstable and ceases to function properly. These mutations are usually recessive in diploid organisms. Temperature sensitive mutants arrange a reversible mechanism[1] and are able to reduce particular gene products at varying stages of growth and are easily done by changing the temperature of growth.
Permissive temperature
editThe permissive temperature is the temperature at which a temperature-sensitive mutant gene product takes on a normal, functional phenotype.[2] When a temperature-sensitive mutant is grown in a permissive condition, the mutant gene product behaves normally (meaning that the phenotype is not observed), even if there is a mutant allele present. This results in the survival of the cell or organism, as if it were a wild type strain. In contrast, the nonpermissive temperature or restrictive temperature is the temperature at which the mutant phenotype is observed.
Temperature sensitive mutations are usually missense mutations, which slightly modifies the energy landscape of the protein folding. The mutant protein will function at the standard, permissive, low temperature. It will alternatively lack the function at a rather high, non-permissive, temperature and display a hypomorphic (partial loss of gene function) and a middle, semi-permissive, temperature.[3]
Use in research
editTemperature-sensitive mutants are useful in biological research. They allow the study of essential processes required for the survival of the cell or organism. Mutations to essential genes are generally lethal and hence temperature-sensitive mutants enable researchers to induce the phenotype at the restrictive temperatures and study the effects. The temperature-sensitive phenotype could be expressed during a specific developmental stage to study the effects.
Examples
editIn the late 1970s, the Saccharomyces cerevisiae secretory pathway, essential for viability of the cell and for growth of new buds, was dissected using temperature-sensitive mutants, resulting in the identification of twenty-three essential genes.[4]
In the 1970s, several temperature-sensitive mutant genes were identified in Drosophila melanogaster, such as shibirets, which led to the first genetic dissection of synaptic function.[5]< In the 1990s, the heat shock promoter hsp70 was used in temperature-modulated gene expression in the fruit fly.[6]
Bacteriophage
editAn infection of an Escherichia coli host cell by a bacteriophage (phage) T4 temperature sensitive (ts) conditionally lethal mutant at a high restrictive temperature generally leads to no phage growth. However, a co-infection under restrictive conditions with two ts mutants defective in different genes generally leads to robust growth because of intergenic complementation. The discovery of ts mutants of phage T4, and the employment of such mutants in complementation tests contributed to the identification of many of the genes in this organism.[7] Because multiple copies of a polypeptide specified by a gene often form multimers, mixed infections with two different ts mutants defective in the same gene often leads to mixed multimers and partial restoration of function, a phenomenon referred to as intragenic complementation. Intragenic complementation of ts mutants defective in the same gene can provide information on the structural organization of the multimer.[8] Growth of phage ts mutants under partially restrictive conditions has been used to identify the functions of genes. Thus genes employed in the repair of DNA damages were identified,[9][10] as well as genes affecting genetic recombination.[11][12] For example, growing a ts DNA repair mutant at an intermediate temperature will allow some progeny phage to be produced. However, if that ts mutant is irradiated with UV light, its survival will be more strongly reduced compared the reduction of survival of irradiated wild-type phage T4.
Conditional lethal mutants able to grow at high temperatures, but unable to grow at low temperatures, were also isolated in phage T4.[13] These cold sensitive mutants defined a discrete set of genes, some of which had been previously identified by other types of conditional lethal mutants.
References
edit- ^ Varadarajan, R.; Nagarajaram, H. A.; Ramakrishnan, C. (1996-11-26). "A procedure for the prediction of temperature-sensitive mutants of a globular protein based solely on the amino acid sequence". Proceedings of the National Academy of Sciences. 93 (24): 13908–13913. Bibcode:1996PNAS...9313908V. doi:10.1073/pnas.93.24.13908. ISSN 0027-8424. PMC 19465. PMID 8943034.
- ^ "Permissive temperature". Biology-Online Dictionary.
- ^ Ben-Aroya, Shay; Pan, Xuewen; Boeke, Jef D.; Hieter, Philip (2010). "Making Temperature-Sensitive Mutants". Guide to Yeast Genetics: Functional Genomics, Proteomics, and Other Systems Analysis. Methods in Enzymology. Vol. 470. pp. 181–204. doi:10.1016/S0076-6879(10)70008-2. ISBN 9780123751720. ISSN 0076-6879. PMC 2957654. PMID 20946811.
- ^ Novick, P.; Field, C.; Schekman, R. (August 1980). "Identification of 23 complementation groups required for post-translational events in the yeast secretory pathway". Cell. 21 (1): 205–215. doi:10.1016/0092-8674(80)90128-2. ISSN 0092-8674. PMID 6996832.
- ^ Yoshihara, Moto; Ito, Kei (March 2012). "Acute Genetic Manipulation of Neuronal Activity for the Functional Dissection of Neural Circuits—A Dream Come True for the Pioneers of Behavioral Genetics". Journal of Neurogenetics. 26 (1): 43–52. doi:10.3109/01677063.2012.663429. PMC 3357893. PMID 22420407.
- ^ Brand, Michael; Jarman, Andrew P.; Jan, Lily Y.; Jan, Yuh Nung (1 September 1993). "asense is a Drosophila neural precursor gene and is capable of initiating sense organ formation". Development. 119 (1): 1–17. doi:10.1242/dev.119.1.1. PMID 8565817.
- ^ Edgar, R. S.; Epstein, R. H. (February 1965). "The Genetics of a Bacterial Virus". Scientific American. 212 (2): 70–79. Bibcode:1965SciAm.212b..70E. doi:10.1038/scientificamerican0265-70. PMID 14272117.
- ^ Bernstein, Harris; Edgar, R S; Denhardt, G H (June 1965). "Intragenic complementation among temperature sensitive mutants of bacteriophage T4D". Genetics. 51 (6): 987–1002. doi:10.1093/genetics/51.6.987. PMC 1210828. PMID 14337770.
- ^ Baldy MW (February 1970). "The UV sensitivity of some early-function temperature-sensitive mutants of phage T4". Virology. 40 (2): 272–287. doi:10.1016/0042-6822(70)90403-4. PMID 4909413.
- ^ Baldy, Marian W.; Strom, Barbara; Bernstein, Harris (March 1971). "Repair of Alkylated Bacteriophage T4 Deoxyribonucleic Acid by a Mechanism Involving Polynucleotide Ligase". Journal of Virology. 7 (3): 407–408. doi:10.1128/JVI.7.3.407-408.1971. PMC 356131. PMID 4927528.
- ^ Bernstein, Harris (10 August 1967). "The effect on recombination of mutational defects in the DNA-polymerase and deoxycytidylate hydroxymethylase of phage T4D". Genetics. 56 (4): 755–769. doi:10.1093/genetics/56.4.755. PMC 1211652. PMID 6061665.
- ^ Bernstein, H. (1 January 1968). "Repair and Recombination in Phage T4. I. Genes Affecting Recombination". Cold Spring Harbor Symposia on Quantitative Biology. 33: 325–331. doi:10.1101/sqb.1968.033.01.037. PMID 4891972.
- ^ Scotti, Paul D. (July 1968). "A new class of temperature conditional lethal mutants of bacteriophage T4D". Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis. 6 (1): 1–14. Bibcode:1968MRFMM...6....1S. doi:10.1016/0027-5107(68)90098-5. PMID 4885498.