title: DNA loop repair by Escherichia coli cell extracts.
abstract: The nick-directed DNA repair efficiency 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 heteroduplex 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 the MutHLS mismatch repair pathway. Strand specificity and repair efficiency 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.
authors.affiliation: School of Medical Technology, College of Medicine, National Taiwan University and Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Republic of China. whfang@ha.mc.ntu.edu.tw
authors.forename: Woei-horng
authors.initials: WH
authors.lastname: Fang
authors.forename: Bo-Jeng
authors.initials: BJ
authors.lastname: Wang
authors.forename: Chiang-Hui
authors.initials: CH
authors.lastname: Wang
authors.forename: Su-Jan
authors.initials: SJ
authors.lastname: Lee
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Chang
authors.forename: Yi-Kuang
authors.initials: YK
authors.lastname: Chuang
authors.forename: Chun-Nan
authors.initials: CN
authors.lastname: Lee
mesh_terms: D001483:Base Sequence; D004260:DNA Repair / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics*; D004270:DNA, Circular / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics*; D005819:Genetic Markers; D010957:Plasmids; D015183:Restriction Mapping
chemical_list: D004269:DNA, Bacterial; D004270:DNA, Circular; D005819:Genetic Markers