title: Suppression of recA deficiency in plasmid recombination by bacteriophage lambda beta protein in RecBCD- ExoI- Escherichia coli cells.
abstract: Plasmid recombination, like other homologous recombination in Escherichia coli, requires RecA protein in most conditions. We have found that the plasmid recombination defect in a recA mutant can be efficiently suppressed by the beta protein of bacteriophage lambda. beta protein is required for homologous recombination of lambda chromosomes during lytic phage growth in a recA host and is known to have a strand-annealing activity resembling that of RecA protein. The bioluminescence recombination assay was used for genetic analysis of beta-protein-mediated plasmid recombination. Efficient suppression of the recA mutation by beta protein required the absence of the E. coli nucleases exonuclease I and RecBCD nuclease. These nucleases inhibit a RecA-mediated plasmid recombination pathway that is more efficient than the pathway functioning in wild-type cells. Like RecA-mediated plasmid recombination in RecBCD- ExoI- cells, beta-protein-mediated plasmid recombination depended on concurrent DNA replication and on the activity of the recQ gene. However, unlike RecA-mediated plasmid recombination, beta-protein-mediated recombination in RecBCD- ExoI- cells was independent of recF and recJ activities. We propose that inactivation of exonuclease I and RecBCD nuclease stabilizes a recombination intermediate that is involved in RecA- and beta-protein-catalyzed homologous pairing reactions. We suggest that the intermediate may be linear plasmid DNA with a protruding 3' end, since these nucleases are known to interfere with the synthesis of such linear forms. The different recF and recJ requirements for beta-protein-dependent and RecA-dependent recombinations imply that the mechanisms of formation or processing of the putative intermediate differ in the two cases.
authors.affiliation: Department of Molecular Genetics, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: I
authors.initials: I
authors.lastname: Berger
authors.forename: A
authors.initials: A
authors.lastname: Cohen
mesh_terms: D001426:Bacterial Proteins / Q000502:physiology; D010582:Bacteriophage lambda / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D005090:Exodeoxyribonucleases / Q000502:physiology; D005798:Genes, Bacterial; D008156:Luciferases / Q000235:genetics; D010957:Plasmids; D011938:Rec A Recombinases / Q000172:deficiency / Q000502:physiology*; D011995:Recombination, Genetic; D013489:Suppression, Genetic; D014764:Viral Proteins / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D014764:Viral Proteins; D008156:Luciferases; D011938:Rec A Recombinases; D005090:Exodeoxyribonucleases; C028450:exodeoxyribonuclease I