DNA mismatch repair (MMR) is a critical mutation surveillance system for recognizing and repairing erroneous insertion, deletion, and disincorporation of base. Major components of mismatch repair system consist of MutH, MutL, and MutS. Dam methylates adenine to distinguish newly synthesized daughter strands from the parent strands. Employing a tyrosine-auxotrophic E. coli FX-11 strain, the mutation frequency can be determined by the number of tyrosine revertants and the cell viability of FX-11 with deficiencies in dam and mismatch repair proteins. This study showed that mutS defect produced a higher mutation frequency than mutH did. Interestingly, double defects in dam and mutS synergistically produced a dramatically higher spontaneous mutation frequency than the summation of mutation frequencies of FX-11 strains with individual deficiency of dam or mutS, suggesting that Dam may work with MutHL to partially accomplish the task of recognizing the mismatch sites to retain partial mismatch repair capacity.

中文翻译：

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Dam，MutH和MutS在大肠杆菌中甲基化导向错配修复中的协同作用。

DNA错配修复（MMR）是用于识别和修复碱基的错误插入，缺失和分解的关键突变监视系统。失配修复系统的主要组件包括MutH，MutL和MutS。大坝甲基化腺嘌呤以区分新合成的子链和母链。使用酪氨酸营养缺陷型大肠杆菌FX-11菌株，突变频率可以由酪氨酸还原剂的数量和FX-11的细胞生存力（大坝和失配修复蛋白缺乏）决定。这项研究表明，mutS缺陷产生的突变频率高于mutH。有趣的是，