[Participation of the HIM1 gene from Saccharomyces cerevisiae in correction of heteroduplex DNA. Molecular cloning of the gene].

A group of Saccharomyces cerevisiae mutants deficient in repair of induced premutation lesions (him mutants) were previously isolated in our laboratory. Recessive him1 mutant had enhanced level of spontaneous and induced mutagenesis as well as specific altered mitotic conversion. This HIM1 gene was supposed to be involved in the process of mismatch correction of heteroduplexes. In this paper the correction efficiency of in vitro constructed heteroduplex DNA in wild-type cells and him1 mutant was studied. In the former cells heteroduplex DNA was repaired highly efficiently (about 90%), this repair efficiency being reduced in him cells approx. two times as compared with the wild-type cells. Molecular cloning of yeast chromosomal DNA fragments containing HIM1 gene was carried out. The clones were selected from the bank of yeast DNA fragments by complementing him1-1 mutation which enhances conversion frequency in ADE2 gene. One of the DNA fragments was analysed by restriction endonuclease digestion and shown to contain an insert of 6 Kb. Chromosomal integrants were obtained by homologous recombination between the plasmid and chromosomal gene him1.