大肠杆菌染色体上终止密码子处的错配修复是独立于GATC甲基化进行的。
Mismatch repair at stop codons is directed independent of GATC methylation on the Escherichia coli chromosome.
作者信息
Sneppen Kim, Semsey Szabolcs
机构信息
Center for Models of Life, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
出版信息
Sci Rep. 2014 Dec 5;4:7346. doi: 10.1038/srep07346.
The mismatch repair system (MMR) corrects replication errors that escape proofreading. Previous studies on extrachromosomal DNA in Escherichia coli suggested that MMR uses hemimethylated GATC sites to identify the newly synthesized strand. In this work we asked how the distance of GATC sites and their methylation status affect the occurrence of single base substitutions on the E. coli chromosome. As a reporter system we used a lacZ gene containing an early TAA stop codon. We found that occurrence of point mutations at this stop codon is unaffected by GATC sites located more than 115 base pairs away. However, a GATC site located about 50 base pairs away resulted in a decreased mutation rate. This effect was independent of Dam methylation. The reversion rate of the stop codon increased only slightly in dam mutants compared to mutL and mutS mutants. We suggest that unlike on extrachromosomal DNA, GATC methylation is not the only strand discrimination signal for MMR on the E. coli chromosome.
错配修复系统（MMR）可纠正逃避校对的复制错误。先前对大肠杆菌染色体外DNA的研究表明，MMR利用半甲基化的GATC位点来识别新合成的链。在这项工作中，我们研究了GATC位点的距离及其甲基化状态如何影响大肠杆菌染色体上单碱基替换的发生。作为报告系统，我们使用了一个含有早期TAA终止密码子的lacZ基因。我们发现，位于超过115个碱基对以外的GATC位点不会影响该终止密码子处点突变的发生。然而，位于约50个碱基对以外的GATC位点会导致突变率降低。这种效应与Dam甲基化无关。与mutL和mutS突变体相比，dam突变体中终止密码子的回复率仅略有增加。我们认为，与染色体外DNA不同，GATC甲基化不是大肠杆菌染色体上MMR的唯一链区分信号。
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