title: Suppression of genetic defects within the RAD6 pathway by srs2 is specific for error-free post-replication repair but not for damage-induced mutagenesis.
abstract: srs2 was isolated during a screen for mutants that could suppress the UV-sensitive phenotype of rad6 and rad18 cells. Genetic analyses led to a proposal that Srs2 acts to prevent the channeling of DNA replication-blocking lesions into homologous recombination. The phenotypes associated with srs2 indicate that the Srs2 protein acts to process lesions through RAD6-mediated post-replication repair (PRR) rather than recombination repair. The RAD6 pathway has been divided into three rather independent subpathways: two error-free (represented by RAD5 and POL30) and one error-prone (represented by REV3). In order to determine on which subpathways Srs2 acts, we performed comprehensive epistasis analyses; the experimental results indicate that the srs2 mutation completely suppresses both error-free PRR branches. Combined with UV-induced mutagenesis assays, we conclude that the Polzeta-mediated error-prone pathway is functional in the absence of Srs2; hence, Srs2 is not required for mutagenesis. Furthermore, we demonstrate that the helicase activity of Srs2 is probably required for the phenotypic suppression of error-free PRR defects. Taken together, our observations link error-free PRR to homologous recombination through the helicase activity of Srs2.
authors.affiliation: Department of Microbiology and Immunology, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5, Canada.
authors.forename: Stacey
authors.initials: S
authors.lastname: Broomfield
authors.forename: Wei
authors.initials: W
authors.lastname: Xiao
mesh_terms: D000251:Adenosine Triphosphatases; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair / Q000235:genetics*; D004261:DNA Replication / Q000187:drug effects / Q000528:radiation effects; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism; D004843:Epistasis, Genetic; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D016296:Mutagenesis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D010641:Phenotype; D011836:Radiation Tolerance / Q000235:genetics; D011995:Recombination, Genetic / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D013489:Suppression, Genetic / Q000235:genetics*; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D014466:Ultraviolet Rays
chemical_list: D005656:Fungal Proteins; C112520:MMS2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C061376:SRS2 protein, S cerevisiae; D008741:Methyl Methanesulfonate; C471606:RAD6 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D004259:DNA-Directed DNA Polymerase; C092602:REV3 protein, S cerevisiae; D000251:Adenosine Triphosphatases; C076225:RAD5 protein, S cerevisiae; D004265:DNA Helicases; D008025:Ligases