Schmidt Kristina H, Viebranz Emilie B, Harris Lorena B, Mirzaei-Souderjani Hamed, Syed Salahuddin, Medicus Robin
Department of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, FL 33620, USA.
Eukaryot Cell. 2010 Feb;9(2):315-24. doi: 10.1128/EC.00260-09. Epub 2009 Dec 11.
Rev3 polymerase and Mph1 DNA helicase participate in error-prone and error-free pathways, respectively, for the bypassing of template lesions during DNA replication. Here we have investigated the role of these pathways and their genetic interaction with recombination factors, other nonreplicative DNA helicases, and DNA damage checkpoint components in the maintenance of genome stability, viability, and sensitivity to the DNA-damaging agent methyl methanesulfonate (MMS). We find that cells lacking Rev3 and Mph1 exhibit a synergistic, Srs2-dependent increase in the rate of accumulating spontaneous, gross chromosomal rearrangements, suggesting that the suppression of point mutations by deletion of REV3 may lead to chromosomal rearrangements. While mph1Delta is epistatic to homologous recombination (HR) genes, both Rad51 and Rad52, but not Rad59, are required for normal growth of the rev3Delta mutant and are essential for survival of rev3Delta cells during exposure to MMS, indicating that Mph1 acts in a Rad51-dependent, Rad59-independent subpathway of HR-mediated lesion bypass. Deletion of MPH1 helicase leads to synergistic DNA damage sensitivity increases in cells with chl1Delta or rrm3Delta helicase mutations, whereas mph1Delta is hypostatic to sgs1Delta. Previously reported slow growth of mph1Delta srs2Delta cells is accompanied by G(2)/M arrest and fully suppressed by disruption of the Mec3-dependent DNA damage checkpoint. We propose a model for replication fork rescue mediated by translesion DNA synthesis and homologous recombination that integrates the role of Mph1 in unwinding D loops and its genetic interaction with Rev3 and Srs2-regulated pathways in the suppression of spontaneous genome rearrangements and in mutation avoidance.
Rev3聚合酶和Mph1 DNA解旋酶分别参与DNA复制过程中绕过模板损伤的易错和无错途径。在此，我们研究了这些途径的作用及其与重组因子、其他非复制性DNA解旋酶以及DNA损伤检查点成分在维持基因组稳定性、活力和对DNA损伤剂甲磺酸甲酯（MMS）敏感性方面的遗传相互作用。我们发现，缺乏Rev3和Mph1的细胞在积累自发的、大规模染色体重排的速率上呈现出协同的、依赖Srs2的增加，这表明通过缺失REV3来抑制点突变可能会导致染色体重排。虽然mph1Δ对同源重组（HR）基因Rad51和Rad52上位，但Rev3Δ突变体的正常生长需要Rad51和Rad52，而不是Rad59，并且在暴露于MMS期间Rev3Δ细胞的存活需要它们，这表明Mph1在HR介导的损伤绕过的Rad51依赖、Rad59非依赖子途径中起作用。MPH1解旋酶的缺失导致chl1Δ或rrm3Δ解旋酶突变细胞中对DNA损伤的敏感性协同增加，而mph1Δ对sgs1Δ下位。先前报道的mph1Δ srs2Δ细胞生长缓慢伴随着G2/M期阻滞，并且通过破坏Mec3依赖的DNA损伤检查点可完全抑制。我们提出了一个由跨损伤DNA合成和同源重组介导的复制叉拯救模型，该模型整合了Mph1在解开D环中的作用及其与Rev3和Srs2调节途径在抑制自发基因组重排和避免突变方面的心遗传相互作用。
