title: Induction of a DNA nickase in the presence of its target site stimulates adaptive mutation in Escherichia coli.
abstract: Adaptive mutation to Lac(+) in Escherichia coli strain FC40 depends on recombination functions and is enhanced by the expression of conjugal functions. To test the hypothesis that the conjugal function that is important for adaptive mutation is the production of a single-strand nick at the conjugal origin, we supplied an exogenous nicking enzyme, the gene II protein (gIIp) of bacteriophage f1, and placed its target sequence near the lac allele. When both gIIp and its target site were present, adaptive mutation was stimulated three- to fourfold. Like normal adaptive mutations, gIIp-induced mutations were recA(+) and ruvC(+) dependent and were mainly single-base deletions in runs of iterated bases. In addition, gIIp with its target site could substitute for conjugal functions in adaptive mutation. These results support the hypothesis that nicking at the conjugal origin initiates the recombination that produces adaptive mutations in this strain of E. coli, and they suggest that nicking may be the only conjugal function required for adaptive mutation.
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
authors.forename: Cesar
authors.initials: C
authors.lastname: Rodriguez
authors.forename: Joshua
authors.initials: J
authors.lastname: Tompkin
authors.forename: Jill
authors.initials: J
authors.lastname: Hazel
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Foster
mesh_terms: D000222:Adaptation, Physiological; D000483:Alleles; D003227:Conjugation, Genetic; D003850:Deoxyribonuclease I / Q000096:biosynthesis*; D004790:Enzyme Induction; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D007763:Lac Operon; D009154:Mutation; D011995:Recombination, Genetic; D014764:Viral Proteins / Q000096:biosynthesis*
chemical_list: C024013:DNA replication complex protein, Bacteriophage lambda; D014764:Viral Proteins; D003850:Deoxyribonuclease I