醫學檢驗暨生物技術學系FANG, WOEI-HORNGWOEI-HORNGFANGWANG, BO-JENGBO-JENGWANGWANG, CHIANG-HUICHIANG-HUIWANGLI, SHU-CHENSHU-CHENLICHANG, YU-TINGYU-TINGCHANGCHUANG, YI-KUANGYI-KUANGCHUANGLEE, CHUN-NANCHUN-NANLEE2009-01-202018-07-062009-01-202018-07-062003http://ntur.lib.ntu.edu.tw//handle/246246/105279The nick-directed DNA repair of a set of M13mp18 derived heteroduplexes containing 8-, 12-, 16-, 22-, 27-, 45-, and 429-nucleotide loops was determined by in vitro assay. Unpaired nucleotides of each heteroduplexes reside within overlapping recognition sites for two restriction endonucleases, permitting independent evaluation of repair occurring on either DNA strand. Our results show that a strand break located either 3’ or 5’ to the loop is sufficient to direct heterology repair to the nicked strand in Escherichia coli extracts. Strand-specific repair by this system requires Mg2+ and the four dNTPs and is equally efficient on insertions and deletions. This activity is distinct from MutHLS mismatch repair pathway. Strand specificity and repair efficiencies are largely independent of the GATC methylation state of the DNA and presence of the products of mismatch repair genes mutH, mutL, and mutS. This study provides evidence for a loop repair pathway in E. coli that is distinct from conventional mismatch repair.en-USDNA REPAIRMISMATCH REPAIRLOOP REPAIRNICK-DIRECTEDESCHERICHIA COLI