Ball Lindsay G, Zhang Ke, Cobb Jennifer A, Boone Charles, Xiao Wei
Department of Microbiology and Immunology, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5.
Mol Microbiol. 2009 Jul;73(1):89-102. doi: 10.1111/j.1365-2958.2009.06748.x. Epub 2009 Jun 1.
DNA post-replication repair (PRR) functions to bypass replication-blocking lesions and prevent damage-induced cell death. PRR employs two different mechanisms to bypass damaged DNA. While translesion synthesis has been well characterized, little is known about the molecular events involved in error-free bypass, although it has been assumed that homologous recombination (HR) is required for such a mode of lesion bypass. We undertook a genome-wide synthetic genetic array screen for novel genes involved in error-free PRR and observed evidence of genetic interactions between error-free PRR and HR. Furthermore, this screen identified and assigned four genes, CSM2, PSY3, SHU1 and SHU2, whose products form a stable Shu complex, to the error-free PRR pathway. Previous studies have indicated that the Shu complex is required for efficient HR and that inactivation of any of these genes is able to suppress the severe phenotypes of top3 and sgs1. We confirmed and further extended some of the reported observations and demonstrated that error-free PRR mutations are also epistatic to sgs1. Based on the above analyses, we propose a model in which error-free PRR utilizes the Shu complex to recruit HR to facilitate template switching, followed by double-Holliday junction resolution by Sgs1-Top3. This mechanism appears to be conserved throughout eukaryotes.
DNA复制后修复(PRR)的功能是绕过复制阻断性损伤并防止损伤诱导的细胞死亡。PRR采用两种不同的机制来绕过受损的DNA。虽然跨损伤合成已得到充分表征,但对于无错误绕过所涉及的分子事件知之甚少,尽管人们认为这种损伤绕过模式需要同源重组(HR)。我们针对参与无错误PRR的新基因进行了全基因组合成遗传阵列筛选,并观察到无错误PRR与HR之间存在遗传相互作用的证据。此外,该筛选确定并将四个基因CSM2、PSY3、SHU1和SHU2(其产物形成稳定的Shu复合物)分配到无错误PRR途径。先前的研究表明,Shu复合物是高效HR所必需的,并且这些基因中的任何一个失活都能够抑制top3和sgs1的严重表型。我们证实并进一步扩展了一些已报道的观察结果,并证明无错误PRR突变对sgs1也是上位性的。基于上述分析,我们提出了一个模型,其中无错误PRR利用Shu复合物招募HR以促进模板切换,随后由Sgs1-Top3解决双Holliday连接。这种机制似乎在整个真核生物中都是保守的。
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