Involvement of RecF pathway recombination genes in postreplication repair in UV-irradiated Escherichia coli cells.

Mutations affecting the RecF pathway of recombination (recF, recG, recJ, recN, recO, recQ, recR, ruvA, ruvC) were systematically introduced into two sets of strains: (a) uvrA and uvrA recA2020, (b) uvrA recBC sbcBC and uvrA recBC sbcBC recA2020. We examined: (i) the effect of these mutations on the repair of DNA daughter-strand gaps which are produced in the nascent DNA synthesized after UV irradiation, and (ii) the ability of recA2020 (a suppressor for the recF mutation) to suppress the UV radiation sensitivity caused by these mutations. In the uvrA cells, mutations in recF, recR or recO genes produced a major deficiency in the repair of daughter-strand gaps, whereas mutations in recJ, recG, recN, recQ, ruvA or ruvC genes had no effect on the repair of daughter-strand gaps. In both uvrA and uvrA recBC sbcBC backgrounds, the UV radiation sensitivity caused by recF, recG, recR, recO, ruvA, or ruvC mutations was partially suppressed by recA2020, whereas the UV radiation sensitivity caused by recJ, recN, or recQ mutations was not suppressed by recA2020. Partial suppression of the UV sensitivity of recG, ruvA and ruvC mutants was not observed with other suppressors for recF, i.e., recA441, recA720 and recA730. Taken together, these results further support the notion that the recF, recR and recO gene products (abbreviated as RecFOR) function at the same step in recombination repair, possible as a complex. It also suggests that this putative RecFOR complex does not contain proteins encoded by other genes involved in the RecF pathway of recombination.

Cosuppression of recF, recR and recO mutations by mutant recA alleles in Escherichia coli cells.

The ability of recA718, recA720, recA730, recA750 and two known recA(Srf) alleles (recA2020 and recA441) to act as suppressors of recF, recR and recO mutations was examined by studying their UV radiation sensitivity in uvrA cells of Escherichia coli. With the exception of recA718, all the mutant recA alleles examined were able to suppress the UV radiation sensitivity caused by recF, recR or recO mutations, but not by the recB mutation. The suppression by recA750 was minimal. The suppression of recF, recR and recO mutations by other recA alleles was more pronounced, but none of them could exert full suppression. Heterozygotes containing a mutant recA allele (recA720, recA730 or recA441) and recA2020 (or recA803, another known recA(Srf) allele) failed to produce any additive or synergistic suppression of recF, indicating that these suppressors did not use different mechanisms for their suppression. Similar to a requirement of recJ+ in the suppression of recF, the suppression of recR and recO mutations by mutant recA alleles also required recJ+. The similar phenotypes conferred by recF, recR, and recO mutations and the observations that a number of mutant recA alleles can cosuppress these three mutations suggest that the recF, recR and recO gene products may function together as a complex.