A new DNA repair gene from Schizosaccharomyces pombe with homology to RecA was identified and characterized. Comparative analysis showed highest similarity to Saccharomyces cerevisiae Rad55p. rhp55+ (rad homologue pombe 55) encodes a predicted 350-amino-acid protein with an Mr of 38,000. The rhp55Δ mutant was highly sensitive to methyl methanesulfonate (MMS), ionizing radiation (IR), and, to a lesser degree, UV. These phenotypes were enhanced at low temperatures, similar to deletions in the S. cerevisiae RAD55 and RAD57 genes. Many rhp55Δ cells were elongated with aberrant nuclei and an increased DNA content. The rhp55 mutant showed minor deficiencies in meiotic intra- and intergenic recombination. Sporulation efficiency and spore viability were significantly reduced. Double-mutant analysis showed that rhp55+ acts in one DNA repair pathway with rhp51+ and rhp54+, homologs of the budding yeast RAD51 and RAD54 genes, respectively. However, rhp55+ is in a different epistasis group for repair of UV-, MMS-, or γ-ray-induced DNA damage than is rad22+, a putative RAD52 homolog of fission yeast. The structural and functional similarity suggests that rhp55+ is a homolog of the S. cerevisiae RAD55 gene and we propose that the functional diversification of RecA-like genes in budding yeast is evolutionarily conserved.

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