Plasmid control of recombination in E. coli K 12

Abstract

The recombination proficiency of three recipient strains of Escherichia coli K12 carrying different plasmids was investigated by conjugal mating with Hfr Cavalli. Some plasmids (e.g. R1drd 19, R6K) caused a marked reduction in the yield of recombinants formed in crosses with Hfr but did not reduce the ability of host strains to accept plasmid F104. The effect of plasmids on recombination was host-dependent. In Hfr crosses with AB1157 (R1-19) used as a recipient the linkage between selected and unselected proximal markers of the donor was sharply decreased. Plasmid R1-19 also decreased the yield of recombinants formed by recF, recL, and recB recC sbcA mutants, showed no effect on the recombination proficiency of recB recC sbcB mutant, and increased the recombination proficiency of recB, recB recC sbcB recF, and recB recC sbcB recL mutants. An ATP-dependent exonuclease activity was found in all tested recB recC mutants carrying plasmid R1-19, while this plasmid did not affect the activity of exonuclease I in strain AB1157 and its rec- derivatives. The same plasmid was also found to protect different rec- derivatives of the strain AB1157 against the lethal action of UV light. We suppose that a new ATP-dependent exonuclease determined by R1-19 plays a role in both repair and recombination of the host through the substitution of or competition with the exoV coded for by the genes recB and recC.

Spontaneous Deletions of Drug-Resistance Determinants from Salmonella Typhimurium in Escherichia Coli

“…If the observed segregations of plasmids from S. typhimuriirnz strains 993 and 16408 were due to legitimate recombination events in E. coli similar to that directed by dar in S. ryphimurium, either a plasmidencoded repressor for such recombination events effective in S. typhimurium but not in E. d i , or a difference in sensitivity of the plasmid to this function in the two species, may be postulated. There are reports which suggest that the plasmids R I -19 and R I00 code for a repressor4 ke molecule that may interact with the E. cwli gene product involved in recombination (Chernin and Ovadis, 1980). Furthermore, these plasmids are stable in E. coli and not in S. fyphirnurium, which has been attributed to the dor gene function of S .…”

Stability of plasmids R1-19 and R100 in hyper-recombinant Escherichia coli strains and in Salmonella typhimurium strains

“…Hfr 22As HB94 but containing plasmid RP4::SuAlP2+ -131G2 (10) As W3110 but containing plasmid RP4::SuA1P2+-P10G2 (10) As GM33 but containing plasmid RP4::SuAlP2+-11G02 (10) As KT01 but containing plasmid RP4::SuA1P2+-P1GP2 homologous recombination generating the Mu recombinants is similar in both E. coli and S. typhimurium recA+ strains. There are reports which suggest that R1-19 and R100 code for a repressor-like molecule that may interact with the E. coli chromosomal gene products involved in recombination (3,4). Such reports raise the possibility that the putative repressor coded by these plasmids may interact with, and repress differently, the E. coli and S. typhimurium recombination enzymes.…”