[Effect of radiosensitivity gene irradiation and genotype on yeast cytoduction]

Effects of gamma- and UV-irradiation of one parent on progenies of yeast crosses are studied. In the crosses of the type: p+ a alc4 X p-alpha ade2 (alc4--nuclear respiration deficiency) zygotic colonies (white) and haploid p+ cytoductant colonies (red) were scored. The irradiation of p+ parent increases the cytoductant frequency up to 17%. When both parents are radiation-sensitive (xrs1, allelic to rad54), the frequency of cytoduction reaches 90%. Crosses p+xrs1 X p-xrs+ or p+xrs+ X p-xrs1 are similar to crosses of wild types. The same results were observed in the case of xrs4 mutants as well as for UV-irradiation. In the progenies of crosses irradiated p+ a alc4 (xrs+ or xrs1) X non-irradiated p-alpha ade2 ura (xrs+ or xrs1) the genotype of red colonies was analysed: in most cases (82.3%-99.8%) they were p+ alpha ade2 ura, that was true haploid cytoductants. It is concluded that irradiation induces particular damages of yeast nuclei leading to a block of normal karyogamy and thus to a cytoductant formation. The highest frequency of cytoduction was observed in crosses of radiosensitive mutants.