We isolated a collection of rec- mutants. The mutant rec41 from this collection was studied in detail. The mutant demonstrated a reduced level of interplasmid recombination, did not grow at the elevated temperature (36 degrees C) and was sensitive to gamma-rays but not to ultraviolet irradiation. The rec41-1 mutation behaved as a semidominant nuclear mutation. Our study on inter- and intraplasmid recombination suggested that the rec41-1 mutation decreased the level of crossing over events significantly and the frequency of gene conversion events at a lower degree. We postulate that rec41 mutation reduces the efficiency of double-stranded break repair and this results in high sensitivity of mutant cells to methylenmethan-sulfonate and ionizing radiation. Using gamma-sensitivity of the mutant cells we isolated a rec41-1 complementing plasmid from a yeast genomic DNA library. The mapping of plasmid integration site allowed us to localize the REC41 gene on the left arm of the VII chromosome nearby LYS4 and CDC43 genes.