Roles of the recG gene product of Escherichia coli in recombination repair: Effects of the .DELTA.recG mutation on cell division and chromosome partition.

Abstract

The products of the recG and ruvAB genes of Escherichia coli are both thought to promote branch migration of Holliday recombination intermediates by their junction specific helicase activities in homologous recombination and recombination repair. To investigate the in vivo role of the recG gene, we examined the effects of a recG null mutation on cell division and chromosome partition. After UV irradiation at a low dose (5J/ m 2 ), ∆recG mutant formed filamentous cells with unpartitioned chromosomes. A mutation in the sfiA gene, which encodes an SOS-inducible inhibitor of septum formation, partially suppressed filamentation of recG mutant cells, but did not prevent the formation of anucleate cells. The sensitivity to UV light and the cytological phenotypes after UV irradiation of a recA recG double mutant were similar to a recA single mutant, consistent with the role of recG, which is assigned to a later stage in recombination repair than recA. The recG ruvAB and recG ruvC double mutants were more sensitive to UV, almost as sensitive as the recA mutant and showed more extreme phenotypes concerning filamentation and chromosome nondisjunction, both after UV irradiation and without UV irradiation than either recG or ruv single mutants. The recG polA12 (Ts) mutant, which is temperature sensitive in growth, formed filamentous cells with centrally located chromosome aggregates when grown at nonpermissive temperature similar to the UV irradiated recG mutant. These results support the notion that RecG is involved in processing Holliday intermediates in recombination repair in vivo. We suggest that the defect in the processing in the recG mutant results in accumulation of nonpartitioned chromosomes, which are linked by Holliday junctions.

Abortive recombination in Escherichia coli ruv mutants blocks chromosome partitioning

“…Genes to Cells (1998) 3, 209-220 217 (Cao & Kogoma 1995;Ishioka et al 1997). It should be noted that ⌬ruvAB and ⌬ruvC mutants showed identical phenotypes as to chromosome nonpartition, accumulation of nonmigrating DNA and UV sensitivity (data not shown), suggesting that all three Ruv proteins work co-operatively in resolving the Holliday junctions.…”

“…We conclude that a major in vivo role of RuvAB and RuvC proteins in repair of UV-induced lesion is the resolution of Holliday recombination intermediates, similar to the assigned role of these proteins in homologous recombination by in vitro studies. A recG mutant is also defective in chromosome partitioning but the defect is milder than for the ruv mutants (Ishioka et al 1997). Since RuvABC and RecG cannot substitute each other, they are not simple alternatives.…”

Penicillin-Binding Protein-Related Factor A Is Required for Proper Chromosome Segregation in Bacillus subtilis

“…Previous work has shown that a prfA mutant (recU::cat) is impaired in homologous recombination independently of other known rec genes (7). Since mutations in genes involved in homologous recombination are known to cause defects in chromosome segregation (15,36,50), it is possible that the chromosome segregation defect of prfA cells is due to a defect in homologous recombination. However, PrfA has no significant primary sequence homology to known recombinases, indicating that the effect of PrfA on homologous recombination may be indirect.…”

Rad62 Protein Functionally and Physically Associates with the Smc5/Smc6 Protein Complex and Is Required for Chromosome Integrity and Recombination Repair in Fission Yeast

“…rad62-1 is synthetically lethal with mutations in the genes promoting recovery from stalled replication, such as rqh1, srs2, and mus81, and those involved in nucleotide excision repair like rad13 and rad16. These results suggest that Rad62, like Rad60, in conjunction with the Smc5-6 complex, plays an essential role in maintaining chromosome integrity and recovery from stalled replication by recombination.Mutants in Schizosaccharomyces pombe rad2, Saccharomyces cerevisiae RAD27, and Escherichia coli polA, all of which are defective in processing Okazaki fragments, are synthetically lethal with mutations in recombination repair genes (8,11,23,24,35,37,40,43,44). In these mutants, double strand breaks (DSBs) are thought to be produced when replication forks encounter the single strand gaps or nicks remaining unsealed due to the inefficient processing of Okazaki fragments, so they require a highly efficient capacity to repair DSBs for survival.…”