Längle-Rouault F, Maenhaut-Michel G, Radman M
EMBO J. 1987 Apr;6(4):1121-7. doi: 10.1002/j.1460-2075.1987.tb04867.x.
Circular heteroduplex DNAs of bacteriophage phi X174 have been constructed carrying either a G:T (Eam+/Eam3) or a G:A (Bam+/Bam16) mismatch and containing either two, one or no GATC sequences. Mismatches were efficiently repaired in wild-type Escherichia coli transfected with phi X174 heteroduplexes only when two unmethylated GATC sequences were present in phi X174 DNA. The requirements for GATC sequences in substrate DNA and for the E. coli MutH function in E. coli mismatch repair can be alleviated by the presence of a persistent nick (transfection with nicked heteroduplex DNA in ligase temperature-sensitive mutant at 40 degrees C). A persistent nick in the GATC sequence is as effective in stimulating mutL- and mutS-dependent mismatch repair as a nick distant from the GATC sequence and from the mismatch. These observations suggest that the MutH protein participates in methyl-directed mismatch repair by recognizing unmethylated DNA GATC sequences and/or stimulating the nicking of unmethylated strands.
噬菌体φX174的环状异源双链DNA已构建完成，其携带一个G:T（Eam+/Eam3）或一个G:A（Bam+/Bam16）错配，且含有两个、一个或没有GATC序列。只有当φX174 DNA中存在两个未甲基化的GATC序列时，用φX174异源双链转染的野生型大肠杆菌中错配才能被有效修复。底物DNA中GATC序列的要求以及大肠杆菌错配修复中大肠杆菌MutH功能的要求可通过存在一个持久性切口来缓解（在40℃下用连接酶温度敏感突变体中的带切口异源双链DNA进行转染）。GATC序列中的一个持久性切口在刺激mutL和mutS依赖性错配修复方面与远离GATC序列和错配的一个切口同样有效。这些观察结果表明，MutH蛋白通过识别未甲基化的DNA GATC序列和/或刺激未甲基化链的切口来参与甲基导向的错配修复。
