Structural specificity in the lethal and mutagenic activity of furocoumarins in yeast cells.

Using monofunctional (Angelicin) and bifunctional furocoumarins (Psoralen and 8 Methoxypsoralen) plus 365 nm light it is shown that both damages, the induced monoadducts and/or crosslinks in DNA, provoke lethal and mutgenic effects in haploid and diploid cells of Saccharomyces cerevisiae. Bifunctional furocoumarins are about 20 times more effective in cell killing than Angelicin. Diploid cells are always more resistant than haploid cells. Dark repair (agar haolding) increases survival. This effect can be at least in part correlated to the release of bound material from DNA in dark repair conditions. Bifunctional psoralens (10 mug/ml) are at least 10-fold more effective in inducing nuclear gene black mutations (his- to HIS+) than Angelicin (10 mug/ml) plus 365 nm light or 254 nm ultraviolet light. In contrast cytoplasmic "petite" (delta-) mutations are about as frequently induced by Angelicin plus 365 nm light as by 254 nm UV light. Bifunctional furocoumarins are less effective. The frequency of cytoplasmic "petite" mutations per survivors decreases during dark repair conditions more efficiently after Angelicin than after Psoralen plus 365 nm light treatment.