2 CDNAS FROM THE PLANT ARABIDOPSIS-THALIANA THAT PARTIALLY RESTORE RECOMBINATION PROFICIENCY AND DNA-DAMAGE RESISTANCE TO ESCHERICHIA-COLI MUTANTS LACKING RECOMBINATION-INTERMEDIATE-RESOLUTION ACTIVITIES

Escherichia coli ruvC recG mutants lack RuvC endonuclease, which resol ves crossed-strand joint molecules (Holliday junctions) formed during homologous recombination into recombinant products, and an activity (R ecG) thought to partially replace RuvC. They are therefore highly defi cient in homologous recombination, and sensitive to UV light and chemi cal DNA-damaging agents, presumably because of inability to tolerate u nrepaired DNA damage by recombinational mechanisms (Lloyd, R.G. (1991) J. Bacteriol. 173:5414 - 5418). We transformed these mutants with pla smids expressing cDNAs from the plant Arabidopsis thaliana. Selection for bacteria with increased resistance to methylmethanesulfonate yield ed two cDNAs, designated DRT111 and DRT112 (DNA-damage-repair/tolerati on). Expression of these plant cDNAs, especially DRT111, restored conj ugal recombination proficiencies in ruvC and ruvC recG mutants to near ly wild-type levels. Both plant cDNAs significantly increased resistan ce of both mutants to UV light and several chemical DNA-damaging agent s, but did not fully correct the mutant phenotypes. Drt111 activity, b ut not Drt112, also increased, to nearly wild-type levels, resistance of recG single mutants to UV plus mitomycin C. The predicted Drt111 an d Drt112 polypeptides, 383 and 167 amino acids respectively, show no s imilarity with one another or with prokaryotic Holliday resolvases. Bo th appear chloroplast targeted; Drt112 is highly homologous to Arabido psis plastocyanin. DRT111 and DRT112 probes hybridize only to DNA from closely related plants.