Altered induction of the adaptive response to alkylation damage in Escherichia coli recF mutants

Abstract

Escherichia coli recF mutants are hypermutable when treated with methyl methanesulfonate (G. C. Walker, Mol. Gen. Genet. 152:93-103, 1977). In this study, methylation hypermutability of recF mutant strains was examined, and it was found that recF+ is required for normal induction of the adaptive response to alkylation damage. Although this regulatory effect of recF mutations results in reduced levels of enzymes that specifically repair methyl lesions in DNA, it only partially explains the hypermutability. Further examination showed that methylation hypermutability of recF mutant strains required a functional umuDC operon, a component of the SOS response. These results lead to the hypothesis that methylation hypermutability results from the effects of recF mutations on the induction of both the SOS response and the adaptive response.The adaptive response of Escherichia coli to alkylation damage involves four known genes arranged in three transcriptional units, the ada-alkB operon and the alkA and aidB genes (for a review, see references 18 and 32). This response is induced when cells are treated with alkylating agents (primarily methylating agents) and the induced activities specifically repair alkylation lesions in DNA. This repair is accomplished by enzymes that either remove methyl groups from modified sites or remove methylated bases from DNA. Induction requires a wild-type ada gene (14) and occurs when Ada protein transfers methyl groups from methylphosphotriesters in the DNA backbone to itself. Methylated Ada protein then binds to a sequence adjacent to the promoter and stimulates transcription of the ada-alkB operon, the alkA gene, and presumably also the aidB gene (22,28). The results presented here show that a wild-type recF gene is required for normal induction of adaptive response genes.Mutations in the recF gene are pleiotropic, affecting recombination, DNA repair, expression of the SOS response, and mutagenesis. The effects of recF mutations on chromosomal recombination are seen in recB recC sbc mutants (12); in this genetic background, recombination requires the wild-type recF gene. recF mutations also have effects on DNA metabolism in wild-type cells; recF is required for recombination between plasmids (8, 13) and for mutagenesis and repair of UV damage to DNA (1,4,6,7,11,12,15,23,24,40). Many of the DNA repair defects associated with recF mutations can be ascribed to their effect on induction of the SOS response, a damage-inducible DNA repair response (5,6,21,(33)(34)(35). The SOS response is induced when RecA protein is activated by DNA damage.Activated RecA then stimulates cleavage of LexA protein, thereby derepressing the SOS genes, which are under the control of the LexA repressor protein (19,20,39,41). Mutations in recF decrease the induction of the SOS response and result in increased sensitivity to DNA-damaging agents (6,21,29,34,35). The role of recF in this regulation is, however, not clear at present. Walker (38) noted that the recF143 mutation also affected mutagenesis by methyl methan...

Evidence for ATP binding and double-stranded DNA binding by Escherichia coli RecF protein

“…Accordingly, we speculate that in the presence of RecO and RecR proteins, the ATP-hydrolyzing activity of RecF protein would be expressed. Alternatively, RecF protein might require only ATP binding rather than hydrolysis to trigger several key regulatory reactions presumed to be needed during DNA repair and recombination (e.g., inducing SOS and adaptive repair responses) (9,20,21,(23)(24)(25)27). Our data suggest that RecF protein possesses independent DNA-and ATP-binding sites.…”

Biochemistry of homologous recombination in Escherichia coli.

“…The RecF gene product is required for recA-dependent postreplication recombinational repair (521,680), plasmidbased mismatch repair (180), and UV-induced recombination (446). RecF activity is also required for efficient induction of the SOS response to DNA damage and for X prophage induction (41,238,420,532,541,542,658,714), as well as for the adaptive response to alkylation damage (656). Expression of some of the genes involved in the RecF pathway of recombination (recN, recQ, and ruv) is under SOS control (357,458,563), yet others (recF, recJ, recO, and recR) are not regulated by the recF-dependent SOS response (41,375,397,445).…”

Sequence and complementation analysis of recF genes from Escherichia coli, Salmonella typhimurium, Pseudomonas putida and Bacillus subtilis: evidence for an essential phosphate binding loop

“…Single mutants in most RecF pathway genes (i.e.recF,O,N,Q,R, ruvA,B) but not recJ (5) are sensitive to UV irradiation. recF single mutants are conjugally recombination proficient (3), deficient in the ability to do plasmid recombination (6), sensitive to UV irradiation (and other DNA damaging agents), deficient in a mutLHS independent pathway of mismatch repair (7), have an attenuated ability to induce the SOS (8) and adaptive responses (9) and are UV-immutable for ssDNA phages (10). Even with these diverse phenotypes, the recF gene has never been identified in a screen for any phenotype other than recombination deficiency.…”