Modulation of DNA Repair and Recombination by the Bacteriophage λ Orf Function in Escherichia coli K-12

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   FIG. 1.

   Partial suppression by Orf of the UV sensitivity phenotype of ruv mutants. The strains are wild type for known recombination and repair functions, except as noted. Symbols for left panel: open triangles, wild type (TP790); filled triangles, galK::orf (TP791); open circles, ruvAB (TP799); filled circles, ruvAB galK::orf (TP800). Symbols for right panel: open triangles, wild type (TP790); filled triangles, galK::orf (TP791); open circles, ruvC (TP801); filled circles, ruvC galK::orf (TP802). Error bars (some of which are smaller than the symbols) indicate standard errors for three measurements of titers.
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   FIG. 2.

   Roles of recombination proteins in the early steps of the Red pathway. DNA intermediates are drawn according to the Stahl model (37). (A) A free dsDNA end is acted on by the Exo-β complex, leaving a 3′-overhanging ssDNA species coated with β. (B) If a complementary ssDNA is available, β pairs the two, generating a spliced recombinant. (C) If a complementary ssDNA is not available, eventually RecORF (or possibly λ Orf) facilitates the polymerization of RecA on the ssDNA, displacing β. (D) The RecA-coated ssDNA can invade an unbroken homologous duplex. Recombinant formation in this case depends upon further processing by RuvABC; this requirement is partially bypassed in the presence of the λ Orf protein.

• American Society for Microbiology