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：2004
卷号：101
期号：25
页码：9315-9320
DOI：10.1073/pnas.0305749101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Recombination between moderately divergent DNA sequences is impaired compared with identical sequences. In yeast, an HO endonuclease-induced double-strand break can be repaired by single-strand annealing (SSA) between flanking homologous sequences. A 3% sequence divergence between 205-bp sequences flanking the double-strand break caused a 6-fold reduction in repair compared with identical sequences. This reduction in heteroduplex rejection was suppressed in a mismatch repair-defective msh6{Delta} strain and partially suppressed in an msh2 separation-of-function mutant. In mlh1{Delta} strains, heteroduplex rejection was greater than in msh6{Delta} strains but less than in wild type. Deleting PMS1, MLH2,or MLH3 had no effect on heteroduplex rejection, but a pms1{Delta} mlh2{Delta} mlh3{Delta} triple mutant resembled mlh1{Delta}. However, correction of the mismatches within heteroduplex SSA intermediates required PMS1 and MLH1 to the same extent as MSH2 and MSH6. An SSA competition assay in which either diverged or identical repeats can be used for repair showed that heteroduplex DNA is likely to be unwound rather than degraded. This conclusion is supported by the finding that deleting the SGS1 helicase also suppressed heteroduplex rejection.
