Comparison of the specificity of ultra-violet and X-rays action on mutability of yeast

Abstract

Red adenineless mutants have been induced in haploid of Saccharomyces cerevisiae by UV- and X-rays. 180 such mutants have proved to be distributed between two loci designed as adᵢ and adz. The adz locus have proved to be more sensitive to mutagenic action of both kinds of radiation than the adᵢ locus. Leaky and nonleaky mutants have been scored in both loci. In adᵢ locus we have considered alleles suppressible and nonsuppressible by the external dominant suppressor. Gene specificity of UV- and X-rays was determined by the ratio (adz mutations / adᵢ mutations). The gene specificity of these two agents appeared to be the same. Intragenic specificity of the mutagens used proved to be the same too. The latter kind of specificity was determined by the ratio (leaky mutations / nonleaky mutations ) both in adᵢ and the adz locus and by ratio ( suppressible mutations / nonsuppressible mutations) in the adᵢ locus. The cause of the different sensitivity to radiation of the loci under consideration is discussed. Two alternative hypotheses have been proposed to explain the impossibility to distinguish UV- and X-rays effects by means of observation of their mutagenic specificity: 1) indirect action of the mutagens used; 2) only one class of mutations, common for both mutagens, was scored. These are the point mutations. Chromosome aberrations by which the effect of UV- and X-rays distinguishable are supposed to be inviable.