Wu T H, Clarke C H, Marinus M G
Department of Pharmacology, University of Massachusetts Medical School, Worcester 01655.
Gene. 1990 Mar 1;87(1):1-5. doi: 10.1016/0378-1119(90)90488-d.
The products of the mutD and mutL genes of Escherichia coli are involved in proofreading by DNA polymerase III and DNA adenine MTase (Dam)-dependent mismatch repair, respectively. We have used the plasmid-borne bacteriophage P22 mnt gene as a target to determine the types of mutations produced in mutL25 and mutD5 strains. Of 60 mutations identified from mutL25 cells, 52 were transition mutations and of these the AT----GC subset predominated (40 out of 52). The majority of AT----GC mutations were found at the same three sites (hotspots). In contrast, transversion mutations (47 out of 76) were found about twice as frequently as transitions (28 out of 76) from mutD5 bacteria. Two hotspots were identified but at different sites than those in the mutL25 cells. These results suggest that the proofreading function of DNA polymerase III primarily repairs potential transversion mutations while Dam-dependent mismatch repair rectifies potential transition mutations.
大肠杆菌mutD和mutL基因的产物分别参与DNA聚合酶III的校对和DNA腺嘌呤甲基转移酶（Dam）依赖性错配修复。我们使用质粒携带的噬菌体P22 mnt基因作为靶点，来确定mutL25和mutD5菌株中产生的突变类型。在从mutL25细胞中鉴定出的60个突变中，52个是转换突变，其中AT→GC亚型占主导（52个中有40个）。大多数AT→GC突变出现在相同的三个位点（热点）。相比之下，从mutD5细菌中发现的颠换突变（76个中有47个）的频率约为转换突变（76个中有28个）的两倍。鉴定出了两个热点，但与mutL25细胞中的位点不同。这些结果表明，DNA聚合酶III的校对功能主要修复潜在的颠换突变，而Dam依赖性错配修复纠正潜在的转换突变。
