Fission yeast homologs of human XPC and CSB, rhp41 and rhp26, are involved in transcription-coupled repair of methyl methanesulfonate-induced DNA damage

Abstract

Methyl methanesulfonate (MMS) methylates nitrogen atoms in purines, and predominantly produces 7-methylguanine and 3-methyladenine (3-meA). Previously, we showed that base excision repair (BER) and nucleotide excision repair (NER) synergistically function to repair MMS-induced DNA damage in the fission yeast Schizosaccharomyces pombe. Here, we studied the roles of NER components in repair of 3-meA and BER intermediates such as the AP site and single strand breaks. Mutants of rhp41 (XPC homolog) and rhp26 (CSB homolog) exhibited moderate sensitivity to MMS. Transcription of the fbp1 gene, which is induced by glucose starvation, was strongly inhibited by MMS damage in rhp41Δ and rhp26Δ strains but not in wild type and 3-meA DNA glycosylase-deficient cells. The results indicate that Rhp41p and Rhp26p are involved in transcriptioncoupled repair (TCR) of MMS-induced DNA damage. In the BER pathway of S. pombe, AP lyase activity of Nth1p mainly incises the AP site to generate a 3′-blocked end, which is in turn converted to 3′-OH by Apn2p. Deletion of rad16 or rhp26 in the nth1Δ strain greatly enhanced MMS sensitivity, suggesting that the AP site could also be corrected by TCR. Double mutant apn2Δ/rad16Δ exhibited hypersensitivity to MMS, implying that Rad16p provides a backup pathway for removal of the 3′-blocked end. Moreover, an rhp51Δ strain was extremely sensitive to MMS and double mutants of nth1Δ/rhp51Δ and apn2Δ/rhp51Δ increased the sensitivity, suggesting that homologous recombination is necessary for repair of three different types of lesions, 3-meA, AP sites and 3′-blocked ends.

Regulation of the Rhp26 ERCC6/CSB chromatin remodeler by a novel conserved leucine latch motif

“…To test the role of Rhp26 in DNA damage repair in vivo, we analyzed the DNA damage sensitivity of S. pombe Rhp26 mutants. Consistent with the literature (28,29), rhp26Δ cells are more sensitive to UV irradiation than wild-type (wt) cells (Fig. 3A).…”

Essential Domains ofSchizosaccharomyces pombeRad8 Required for DNA Damage Response

“…The first group is specifically sensitive to MMS, consisting only of rad8∆ itself and rhp26∆ , the ortholog of Sc Rad26 associated with transcription-coupled repair (Kanamitsu and Ikeda 2011). Group 2 mutants were only sensitive to CPT treatment, but not the other agents.…”

“…Of the four remaining phenotypic groups, the first group is defined by rad8∆ , and is sensitive primarily to MMS. It contains one other helicase mutant, rhp26∆ , required for transcription-coupled repair (Kanamitsu and Ikeda 2011). Not surprisingly, a double mutant rad8∆ rhp26∆ showed dramatically increased sensitivity.…”

A snapshot of Snf2 enzymes in fission yeast

“…Viable Mutant sensitive to UV and ionizing radiation [37] SPCC330.01c Rhp16 Viable Nucleotide excision repair [38,39] SPAC17A2.12 Rrp1 Ris1…”

“…Although both of these enzymes are essential for meiotic recombination, Rhp54 has been found to be specifically degraded by the ubiquitin-mediated pathway in the G 1 -phase of the cell cycle. Mutations in rad8 result in sensitization of cells towards UV and ionizing radiation [37], whereas the rhp16 and rhp26 mutant shows intermediate UV radiation sensitivity and the Rhp16 and Rhp26 proteins are involved in the nucleotide excision repair pathway [38,39]. The meiotic DSB repair pathway, resistance to genotoxic reagents and ionizing radiation are significantly compromised in double deletion strains of rhp54 and rdh54 [32][33][34].…”