Induction of Mitotic Crossing over in Saccharomyces Cereviszae by Breakdown Products of Dimethylnitros- Amine, Diethylnitrosamine, I-naphthylamine and 2-naphthylamine Formed by an in Vitro Hydroxylation System
نویسنده
چکیده
Dimethylnitrosamine and diethylnitrosamine, two potent carcinogens, are nonmutagenic when tested directly in microorganisms. Likewise l-naphthylamine and 2-naphthylamine are also nonmutagenic but the N-hydroxy derivatives are mutagenic in microorganisms. Apparently these compounds require metabolism to breakdown products which are then the proximately active agents, and microorganisms lack the enzymes necessary to effect this conversion. These compounds are mutagenic in Saccharomyces after conversion to breakdown products in an in vitro hydroxylation medium. The induction of mitotic crossing over in Saccharomyces cereuisiae by breakdown products of dimethylnitrosamine, diethylnitrosamine, 1-naphthylamine and 2-naphthylamine formed in the UDENFRIEND hydroxylation medium is reported in this communication. Mitotic crossing over was detected as red sectored colonies resulting from induced homozygosity of the ade2 marker. Dimethylamine and diethylamine, which lack the nitroso group of the nitrosamines, did not induce mitotic crossing over under any of the test conditions. To further confirm that the induced sectored colonies were the result of mitotic crossing over they were tested for the presence of reciprocal products. The expected reciprocal products were found in over 67% of the isolates tested. The significance and practicality of using mitotic recombination as an indicator of genetic damage potential of chemicals is discussed. ITOTIC recombination has been observed in a variety of diploid organisms (STERN 1936; PONTECORVO et al. 1953; JAMES and LEE-WHITING 1955; HOLLIDAY 1961; FJELD and STROMANES 1965) and probably in mammals as well (GRUNEBERG 1966; BATEMAN 1967). The potential result of a recombinational event is the generation of a new genotype by crossing over followed by appropriate segregation of the products of mitosis. The consequence to biological systems for such an event is the expression of a detrimental phenotype in the homozygous condition which goes undetected while heterozygous (ZIMMERMAN 1971 b) . A number of chemicals which are known mutagens and carcinogens cause, in Geneucs 74 : 433-44.2 July, 1973
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