Carraway M, Marinus M G
Department of Pharmacology, University of Massachusetts Medical School, Worcester 01655.
J Bacteriol. 1993 Jul;175(13):3972-80. doi: 10.1128/jb.175.13.3972-3980.1993.
The fate of heteroduplex molecules containing 5-, 7-, 9-, 192-, 410-, and 514-base loops after transformation of wild-type and various mutant strains of Escherichia coli has been examined. No evidence for repair was obtained for the wild type or for strains with mutations in the following genes: mutS, recA, recBC sbcBC, recD, recF, recJ, recN, recO, recR, recBC sbcBC recF uvrA, recG ruvC, ruvB, lexA3, lexA51, uvrA, nfo xth nth, polA(Ts), or pcnB. These results rule out the involvement of the SOS system and most known recombination and repair pathways. Repair of heteroduplex molecules containing 410- and 514-base loops was observed when a 1-base deletion-insertion mismatch was present nearby. The repair of both the mismatch and the loops was directed by the state of dam methylation of the DNA chains and was dependent on the product of the mutS gene. A high efficiency of repair (95%) was found even when the mismatch and the loops were 1,448 nucleotides apart. We conclude that multibase loops in DNA can be removed only as a consequence of corepair by dam-directed mismatch repair.
研究了含有5个、7个、9个、192个、410个和514个碱基环的异源双链分子在野生型及大肠杆菌各种突变菌株转化后的命运。未获得野生型或以下基因突变菌株存在修复的证据：mutS、recA、recBC sbcBC、recD、recF、recJ、recN、recO、recR、recBC sbcBC recF uvrA、recG ruvC、ruvB、lexA3、lexA51、uvrA、nfo xth nth、polA（Ts）或pcnB。这些结果排除了SOS系统以及大多数已知重组和修复途径的参与。当附近存在1个碱基的缺失-插入错配时，观察到含有410个和514个碱基环的异源双链分子的修复。错配和环的修复均由DNA链的dam甲基化状态指导，并依赖于mutS基因的产物。即使错配和环相隔1448个核苷酸，也发现了高效的修复（95%）。我们得出结论，DNA中的多碱基环只能作为由dam指导的错配修复的共修复结果而被去除。
