[Molecular nature of the direct mutations induced by 4-nitro-quinoline-N-oxide and 3-methyl-4-nitroquinoline-N-oxide in the ADE2 gene of Saccharomyces cerevisiae].

The lethal and mutagenic effects and the nature of forward mutations in ADE2 gene induced by highly carcinogenic agent 4-nitroquinoline-N-oxide (4NQO) and its noncarcinogenic analogue 3-methyl-4-nitroquinoline-N-oxide (3M4NQO) have been examined in Saccharomyces cerevisiae. It is shown that 3M4NQO is more toxic than 4NQO. Both are very efficient mutagens: the mutagenic efficiency for ADE1 and ADE2 genes was 7.9 X 10(-5) for 4NQO and 10.5 X 10(-5) for 3M4NQO. The base pair substitutions are the main type of induced mutations in ADE2 gene (95 and 89% for 4NQO and 3M4NQO, respectively); among these 40% transversions for 4NQO and 63% for 3M4NQO, GC----AT transitions-32 and 31% for 4NQO and 3M4NQO, respectively, AT----GC transitions-23 and 22% for 4NQO and 3M4NQO, respectively. The results obtained indicate that 4NQO and 3M4NQO induce the same spectrum of mutations in ADE2 gene and that both mutagens are nonspecific in yeast cells.