GENETIC EFFECTS OF POLYNUCLEAR HYDROCARBONS - INDUCTION OF MITOTIC GENE CONVERSION

Five polynuclear hydrocarbons were tested for their ability to induce mitotic gene conversion in a diploid strain of the yeast Saccharomyces cerevisiae. Mitotic gene conversion is a process which causes genetic variegation in somatic cells by the interaction of two different alleles of the same gene due to a presumably localized pairing of homologous chromosomes. To enhance the sensitivity of the test system the diploid strain used was also made respiratory deficient. Such a strain, in the absence of a fermentable substrate, was rapidly deprived of energy sources and consequently unable to repair DNA damage. Under such conditions mitotic gene conversion was induced by 9:10-dimethylbenzanthracene but not with pyrene, 3:4-benzpyrene, 1:2-benzanthracene and 1:2, 5:6-dibenzanthracene. The inactivity of the latter compounds was ascribed to either their inability to react directly with DNA or else to the lack of activating enzymes in the yeast cells used. The results are discussed in the light of a general genetic theory of carcinogenesis including both karyotic genetic effects like mutation, mitotic recombination and mitotic gene conversion, as well as cytoplasmic mutation. © 1969 Springer-Verlag.