Abstract
Yeast DNA postreplication repair (PRR) bypasses replication-blocking lesions to prevent damage-induced cell death. PRR employs two different mechanisms to bypass damaged DNA, namely translesion synthesis (TLS) and error-free PRR, which are regulated via sequential ubiquitination of proliferating cell nuclear antigen (PCNA). We previously demonstrated that error-free PRR utilizes homologous recombination to facilitate template switching. To our surprise, genes encoding the Mre11-Rad50-Xrs2 (MRX) complex, which are also required for homologous recombination, are epistatic to TLS mutations. Further genetic analyses indicated that two other nucleases involved in double-strand end resection, Sae2 and Exo1, are also variably required for efficient lesion bypass. The involvement of the above genes in TLS and/or error-free PRR could be distinguished by the mutagenesis assay and their differential effects on PCNA ubiquitination. Consistent with the observation that the MRX complex is required for both branches of PRR, the MRX complex was found to physically interact with Rad18 in vivo. In light of the distinct and overlapping activities of the above nucleases in the resection of double-strand breaks, we propose that the interplay between distinct single-strand nucleases dictate the preference between TLS and error-free PRR for lesion bypass.
Highlights
In order to maintain genomic integrity, living organisms have developed a set of highly conserved mechanisms to deal with spontaneous and induced DNA damage
Upon further screening and characterization of the MRX complex, we found that null mutations of mre11 (Figure 1A), rad50 (Figure 1B) and xrs2 (Figure 1C) are essentially epistatic to rev3 with respect to killing by the alkylating agent methyl methanesulfonate (MMS) that causes replication-blocking lesions, which was in sharp contrast to the synergistic interactions between hr and rev3 mutations [10]
This study offers a greater understanding of how translesion DNA synthesis (TLS) and error-free postreplication repair (PRR) are co-ordinately operated at the molecular level
Summary
In order to maintain genomic integrity, living organisms have developed a set of highly conserved mechanisms to deal with spontaneous and induced DNA damage. The mre11 mms2 rev3 triple mutant is more sensitive to DNA damage than either mre11 single or the mms2 rev3 double mutant (Figure 2C), indicating that Mre11 does confer an additional function independent of PCNA mono- and polyubiquitination at the K164 residue.
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