Two cDNAs from the plant Arabidopsis thaliana that partially restore recombination proficiency and DNA-damage resistance to E. coli mutants lacking recombination-intermediate-resolution activities.

Escherichia coli ruvC recG mutants lack RuvC endonuclease, which resolves crossed-strand joint molecules (Holliday junctions) formed during homologous recombination into recombinant products, and an activity (RecG) thought to partially replace RuvC. They are therefore highly deficient in homologous recombination, and sensitive to UV light and chemical DNA-damaging agents, presumably because of inability to tolerate unrepaired DNA damage by recombinational mechanisms (Lloyd, R.G. (1991) J. Bacteriol. 173:5414-5418). We transformed these mutants with plasmids expressing cDNAs from the plant Arabidopsis thaliana. Selection for bacteria with increased resistance to methylmethanesulfonate yielded two cDNAs, designated DRT111 and DRT112 (DNA-damage-repair/toleration). Expression of these plant cDNAs, especially DRT111, restored conjugal recombination proficiencies in ruvC and ruvC recG mutants to nearly wild-type levels. Both plant cDNAs significantly increased resistance of both mutants to UV light and several chemical DNA-damaging agents, but did not fully correct the mutant phenotypes. Drt111 activity, but not Drt112, also increased, to nearly wild-type levels, resistance of recG single mutants to UV plus mitomycin C. The predicted Drt111 and Drt112 polypeptides, 383 and 167 amino acids respectively, show no similarity with one another or with prokaryotic Holliday resolvases. Both appear chloroplast targeted; Drt112 is highly homologous to Arabidopsis plastocyanin. DRT111 and DRT112 probes hybridize only to DNA from closely related plants.