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：2015
卷号：112
期号：50
页码：E6898-E6906
DOI：10.1073/pnas.1507386112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceWe integrated single-molecule superresolution imaging with biochemical and genomic approaches to understand how the mismatch repair protein MutS efficiently identifies DNA mismatches during real time in living cells. We show that MutS molecules move fast, exploring the entire nucleoid, but can transition to a slow-moving population that is localized at the replisome even before a mismatch is produced. We show that bacterial MutS must initiate mismatch binding in very close proximity to the replisome. We also show that mismatch detection increases MutS speed, supporting the model for MutS sliding clamp formation after mismatch recognition. Our results provide fundamental insight into the searching behavior of single MutS molecules during DNA replication in live cells. MutS is responsible for initiating the correction of DNA replication errors. To understand how MutS searches for and identifies rare base-pair mismatches, we characterized the dynamic movement of MutS and the replisome in real time using superresolution microscopy and single-molecule tracking in living cells. We report that MutS dynamics are heterogeneous in cells, with one MutS population exploring the nucleoid rapidly, while another MutS population moves to and transiently dwells at the replisome region, even in the absence of appreciable mismatch formation. Analysis of MutS motion shows that the speed of MutS is correlated with its separation distance from the replisome and that MutS motion slows when it enters the replisome region. We also show that mismatch detection increases MutS speed, supporting the model for MutS sliding clamp formation after mismatch recognition. Using variants of MutS and the replication processivity clamp to impair mismatch repair, we find that MutS dynamically moves to and from the replisome before mismatch binding to scan for errors. Furthermore, a block to DNA synthesis shows that MutS is only capable of binding mismatches near the replisome. It is well-established that MutS engages in an ATPase cycle, which is necessary for signaling downstream events. We show that a variant of MutS with a nucleotide binding defect is no longer capable of dynamic movement to and from the replisome, showing that proper nucleotide binding is critical for MutS to localize to the replisome in vivo. Our results provide mechanistic insight into the trafficking and movement of MutS in live cells as it searches for mismatches.
