期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2009
卷号：106
期号：23
页码：9356-9361
DOI：10.1073/pnas.0902793106
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Double-strand breaks (DSBs) in DNA are lethal unless repaired. Faithful repair requires processing of the DSB ends and interaction with intact homologous DNA, which can produce genetic recombinants. To determine the role of nucleases in DSB end-processing and joint molecule resolution, we studied recombination at the site of a single DSB, generated by induction of the I-SceI endonuclease, during meiosis of fission yeast lacking Rec12 (Spo11 homolog) and, hence, other DSBs. We find that in the presence of the MRN (Rad32-Rad50-Nbs1) complex efficient recombination requires Ctp1, the ortholog of the nuclease Sae2, but not the nuclease activity of MRN. In the absence of MRN, exonuclease 1 (Exo1) becomes the major nuclease required for efficient recombination. Our data indicate that MRN enables access of Ctp1 to the DSB but blocks access of Exo1. In our assay, the Rad16-Swi10 nuclease, required for nucleotide excision-repair, is required for efficient recombination, presumably to remove heterologous DNA at the end of the I-SceI cut site. Another nuclease, the Mus81-Eme1 Holliday junction resolvase, is required to generate crossovers accompanying gene conversion at the I-SceI cut site. Additional, previously published evidence indicates that these 5 nucleases play similar roles in wild-type fission yeast meiotic recombination and in the repair of spontaneous and damage-induced mitotic DSBs. We propose that in wild-type meiosis MRN, in conjunction with Ctp1, removes the covalently attached Rec12 protein from the DNA end, which is then resected by Ctp1 and other activities to produce the single-stranded DNA necessary for further steps of DSB repair.
