A plant cDNA that partially complements Escherichia coli recA mutations predicts a polypeptide not strongly homologous to RecA proteins.

A plant (Arabidopsis thaliana) cDNA previously selected for its ability to partially complement the UV sensitivity of Escherichia coli RecA-UvrC-Phr- mutants and designated DRT100 (DNA-damage repair/toleration) was subcloned into a high-copy-number plasmid and expressed via a bacterial promotor. It increased resistance of RecA-UvrB-Phr- bacteria to mitomycin C and methyl methanesulfonate as well as to UV light. This lack of specificity, and its ability to increase resistance in both UvrB- and UvrC- mutants, suggested that Drt100 activity might be complementing RecA- phenotypes. DRT100 partially complemented three RecA- phenotypes thought to reflect deficiencies in homologous recombination--namely, inability to plate lambda red-gam- phages and P1 phages and to recombinationally integrate donor DNA during conjugal crosses--but did not complement inability to induce E. coli SOS functions. The 395-amino acid DRT100 open reading frame encodes an apparent N-terminal chloroplast transit peptide and a putative 322-residue mature protein with a conserved nucleotide binding motif, but otherwise little global homology with bacterial RecA proteins. There are several tandemly repeated leucine-rich motifs. DNA from two closely related plants, but not from maize, hybridized strongly to a DRT100 cDNA probe.