The aim of this study was to investigate structural contributions to the maintenance of rotors in... more The aim of this study was to investigate structural contributions to the maintenance of rotors in human atrial fibrillation (AF) and possible mechanisms of termination. Methods and results A three-dimensional human biatrial finite element model based on patient-derived computed tomography and arrhythmia observed at electrophysiology study was used to study AF. With normal physiological electrical conductivity and effective refractory periods (ERPs), wave break failed to sustain reentrant activity or electrical rotors. With depressed excitability, decreased conduction anisotropy, and shorter ERP characteristic of AF, reentrant rotors were readily maintained. Rotors were transiently or permanently trapped by fibre discontinuities on the lateral wall of the right atrium near the tricuspid valve orifice and adjacent to the crista terminalis, both known sites of right atrial arrhythmias. Modelling inexcitable regions near the rotor tip to simulate fibrosis anchored the rotors, converting the arrhythmia to macro-reentry. Accordingly, increasing the spatial core of inexcitable tissue decreased the frequency of rotation, widened the excitable gap, and enabled an external wave to impinge on the rotor core and displace the source. Conclusion These model findings highlight the importance of structural features in rotor dynamics and suggest that regions of fibrosis may anchor fibrillatory rotors. Increasing extent of fibrosis and scar may eventually convert fibrillation to excitable gap reentry. Such macro-reentry can then be eliminated by extending the obstacle or by external stimuli that penetrate the excitable gap.
The HIV positive selection mutation database is a large-scale database available at http://www. b... more The HIV positive selection mutation database is a large-scale database available at http://www. bioinformatics.ucla.edu/HIV/ that provides detailed selection pressure maps of HIV protease and reverse transcriptase, both of which are molecular targets of antiretroviral therapy. This database makes available for the first time a very large HIV sequence dataset (sequences from $50 000 clinical AIDS samples, generously contributed by Specialty Laboratories, Inc.), which makes possible highresolution selection pressure mapping. It provides information about not only the selection pressure on individual sites but also how selection pressure at one site is affected by mutations on other sites. It also includes datasets from other public databases, namely the Stanford HIV database [
Although many human immunodeficiency virus type 1 (HIV-1)-infected persons are treated with multi... more Although many human immunodeficiency virus type 1 (HIV-1)-infected persons are treated with multiple protease inhibitors in combination or in succession, mutation patterns of protease isolates from these persons have not been characterized. We collected and analyzed 2,244 subtype B HIV-1 isolates from 1,919 persons with different protease inhibitor experiences: 1,004 isolates from untreated persons, 637 isolates from persons who received one protease inhibitor, and 603 isolates from persons receiving two or more protease inhibitors. The median number of protease mutations per isolate increased from 4 in untreated persons to 12 in persons who had received four or more protease inhibitors. Mutations at 45 of the 99 amino acid positions in the protease—including 22 not previously associated with drug resistance—were significantly associated with protease inhibitor treatment. Mutations at 17 of the remaining 99 positions were polymorphic but not associated with drug treatment. Pairs and...
Summary: Direct PCR sequencing on genetic material containing allelic mixtures results in sequenc... more Summary: Direct PCR sequencing on genetic material containing allelic mixtures results in sequences containing ambiguous nucleotides. Because codons exhibiting allelic mixtures present evidence of evolutionary pressure, it is important to include this information in the assessment of codon synonymy. We developed a program, ‘Synonymous–Nonsynonymous Mutation Rates between Sequences Containing Ambiguous Nucleotides’ (Syn-SCAN), that calculates synonymous and non-synonymous substitution rates using a model that includes allelic mixtures. Availability: Syn-SCAN is implemented on the web and can be downloaded from http://hivdb.stanford.edu Contact: [email protected] * To whom correspondence should be addressed.
A system to determine if HIV-reverse transcriptase (RT) base misincorporations can promote strand... more A system to determine if HIV-reverse transcriptase (RT) base misincorporations can promote strand transfer was constructed. A donor RNA, on which RT-directed DNA synthesis was initiated, shared homology over a 119 base internal region with an acceptor RNA, to which DNAs initiated on the donor could transfer. Products completed on the donor in the presence or absence of acceptor were isolated and PCR was used to amplify these DNAs. PCR products were ligated into a vector which had this same region (near the N-terminus of the ␣lac gene) removed. Transformed E. coli were screened in an ␣-complementation assay by blue-white phenotype analysis with white colonies scored as those with errors in plasmid-derived ␣-lac. The frequence of white colonies +/− standard deviations was 0.031 +/− 0.006 and 0.0037 +/− 0.009, for plasmids with inserts derived from donor-directed products synthesized with 100 M dNTPs in the presence and absence of acceptor template, respectively. Statistical analysis indicated a lower white colony frequency in the presence of acceptor (p = 0.0025). The lower frequency with acceptor implies that a portion of the errors made on the donor are transferred to the acceptor suggesting that base misincorporations can induce strand transfer.
Mutations selected or deselected during passage of human immunodeficiency virus strain HXB2 or re... more Mutations selected or deselected during passage of human immunodeficiency virus strain HXB2 or resistant variants with tenofovir (TFV), abacavir (ABC), and lamivudine (3TC) differed depending on the drug combination and virus genotype. In the wild-type virus, TFV-ABC and TFV-3TC selected K65R (with reduced susceptibility to all three inhibitors) and then Y115F. TFV-containing regimens might increase K65R selection, which confers multiple nucleoside reverse transcriptase inhibitor resistance.
The aim of this study was to investigate structural contributions to the maintenance of rotors in... more The aim of this study was to investigate structural contributions to the maintenance of rotors in human atrial fibrillation (AF) and possible mechanisms of termination. Methods and results A three-dimensional human biatrial finite element model based on patient-derived computed tomography and arrhythmia observed at electrophysiology study was used to study AF. With normal physiological electrical conductivity and effective refractory periods (ERPs), wave break failed to sustain reentrant activity or electrical rotors. With depressed excitability, decreased conduction anisotropy, and shorter ERP characteristic of AF, reentrant rotors were readily maintained. Rotors were transiently or permanently trapped by fibre discontinuities on the lateral wall of the right atrium near the tricuspid valve orifice and adjacent to the crista terminalis, both known sites of right atrial arrhythmias. Modelling inexcitable regions near the rotor tip to simulate fibrosis anchored the rotors, converting the arrhythmia to macro-reentry. Accordingly, increasing the spatial core of inexcitable tissue decreased the frequency of rotation, widened the excitable gap, and enabled an external wave to impinge on the rotor core and displace the source. Conclusion These model findings highlight the importance of structural features in rotor dynamics and suggest that regions of fibrosis may anchor fibrillatory rotors. Increasing extent of fibrosis and scar may eventually convert fibrillation to excitable gap reentry. Such macro-reentry can then be eliminated by extending the obstacle or by external stimuli that penetrate the excitable gap.
The HIV positive selection mutation database is a large-scale database available at http://www. b... more The HIV positive selection mutation database is a large-scale database available at http://www. bioinformatics.ucla.edu/HIV/ that provides detailed selection pressure maps of HIV protease and reverse transcriptase, both of which are molecular targets of antiretroviral therapy. This database makes available for the first time a very large HIV sequence dataset (sequences from $50 000 clinical AIDS samples, generously contributed by Specialty Laboratories, Inc.), which makes possible highresolution selection pressure mapping. It provides information about not only the selection pressure on individual sites but also how selection pressure at one site is affected by mutations on other sites. It also includes datasets from other public databases, namely the Stanford HIV database [
Although many human immunodeficiency virus type 1 (HIV-1)-infected persons are treated with multi... more Although many human immunodeficiency virus type 1 (HIV-1)-infected persons are treated with multiple protease inhibitors in combination or in succession, mutation patterns of protease isolates from these persons have not been characterized. We collected and analyzed 2,244 subtype B HIV-1 isolates from 1,919 persons with different protease inhibitor experiences: 1,004 isolates from untreated persons, 637 isolates from persons who received one protease inhibitor, and 603 isolates from persons receiving two or more protease inhibitors. The median number of protease mutations per isolate increased from 4 in untreated persons to 12 in persons who had received four or more protease inhibitors. Mutations at 45 of the 99 amino acid positions in the protease—including 22 not previously associated with drug resistance—were significantly associated with protease inhibitor treatment. Mutations at 17 of the remaining 99 positions were polymorphic but not associated with drug treatment. Pairs and...
Summary: Direct PCR sequencing on genetic material containing allelic mixtures results in sequenc... more Summary: Direct PCR sequencing on genetic material containing allelic mixtures results in sequences containing ambiguous nucleotides. Because codons exhibiting allelic mixtures present evidence of evolutionary pressure, it is important to include this information in the assessment of codon synonymy. We developed a program, ‘Synonymous–Nonsynonymous Mutation Rates between Sequences Containing Ambiguous Nucleotides’ (Syn-SCAN), that calculates synonymous and non-synonymous substitution rates using a model that includes allelic mixtures. Availability: Syn-SCAN is implemented on the web and can be downloaded from http://hivdb.stanford.edu Contact: [email protected] * To whom correspondence should be addressed.
A system to determine if HIV-reverse transcriptase (RT) base misincorporations can promote strand... more A system to determine if HIV-reverse transcriptase (RT) base misincorporations can promote strand transfer was constructed. A donor RNA, on which RT-directed DNA synthesis was initiated, shared homology over a 119 base internal region with an acceptor RNA, to which DNAs initiated on the donor could transfer. Products completed on the donor in the presence or absence of acceptor were isolated and PCR was used to amplify these DNAs. PCR products were ligated into a vector which had this same region (near the N-terminus of the ␣lac gene) removed. Transformed E. coli were screened in an ␣-complementation assay by blue-white phenotype analysis with white colonies scored as those with errors in plasmid-derived ␣-lac. The frequence of white colonies +/− standard deviations was 0.031 +/− 0.006 and 0.0037 +/− 0.009, for plasmids with inserts derived from donor-directed products synthesized with 100 M dNTPs in the presence and absence of acceptor template, respectively. Statistical analysis indicated a lower white colony frequency in the presence of acceptor (p = 0.0025). The lower frequency with acceptor implies that a portion of the errors made on the donor are transferred to the acceptor suggesting that base misincorporations can induce strand transfer.
Mutations selected or deselected during passage of human immunodeficiency virus strain HXB2 or re... more Mutations selected or deselected during passage of human immunodeficiency virus strain HXB2 or resistant variants with tenofovir (TFV), abacavir (ABC), and lamivudine (3TC) differed depending on the drug combination and virus genotype. In the wild-type virus, TFV-ABC and TFV-3TC selected K65R (with reduced susceptibility to all three inhibitors) and then Y115F. TFV-containing regimens might increase K65R selection, which confers multiple nucleoside reverse transcriptase inhibitor resistance.
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