title: Conjugational hyperrecombination achieved by derepressing the LexA regulon, altering the properties of RecA protein and inactivating mismatch repair in Escherichia coli K-12.
abstract: The frequency of recombinational exchanges (FRE) that disrupt co-inheritance of transferred donor markers in Escherichia coli Hfr by F(-) crosses differs by up to a factor of two depending on physiological factors and culture conditions. Under standard conditions we found FRE to be 5.01 +/- 0.43 exchanges per 100-min units of DNA length for wild-type strains of the AB1157 line. Using these conditions we showed a cumulative effect of various mutations on FRE. Constitutive SOS expression by lexA gene inactivation (lexA71::Tn5) and recA gene mutation (recA730) showed, respectively, approximately 4- and 7-fold increases of FRE. The double lexA71 recA730 combination gave an approximately 17-fold increase in FRE. Addition of mutS215::Tn10, inactivating the mismatch repair system, to the double lexA recA mutant increased FRE to approximately 26-fold above wild-type FRE. Finally, we showed that another recA mutation produced as much SOS expression as recA730 but increased FRE only 3-fold. We conclude that three factors contribute to normally low FRE under standard conditions: repression of the LexA regulon, the properties of wild-type RecA protein, and a functioning MutSHL mismatch repair system. We discuss mechanisms by which the lexA, recA, and mutS mutations may elevate FRE cumulatively to obtain hyperrecombination.
authors.affiliation: Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85721-0106, USA.
authors.forename: Vladislav A
authors.initials: VA
authors.lastname: Lanzov
authors.forename: Irina V
authors.initials: IV
authors.lastname: Bakhlanova
authors.forename: Alvin J
authors.initials: AJ
authors.lastname: Clark
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D003227:Conjugation, Genetic; D004260:DNA Repair; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D051719:MutS DNA Mismatch-Binding Protein; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000235:genetics* / Q000378:metabolism; D000099160:LexA Repressor Protein
chemical_list: D000251:Adenosine Triphosphatases; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D051719:MutS DNA Mismatch-Binding Protein; D011938:Rec A Recombinases; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein; C497175:MutS protein, E coli