Direct and indirect effects of ultraviolet light on the mutagenesis of parvovirus H-1 in human cells.

U.v. radiation is directly mutagenic for the single-stranded DNA parvovirus H-1 propagated in human cells. Mutation induction in the progeny of u.v.-irradiated virus increased linearly with the dose and could be ascribed neither to an increased number of rounds of viral replication nor to the indirect activation of an inducible cellular mutator activity by the u.v.-damaged virus. The level of mutagenesis among the descendants of both unirradiated and u.v.-damaged H-1 was enhanced if the host cells had been exposed to sublethal doses of u.v. light before infection. This indirect enhancement of viral mutagenesis in pre-irradiated cells was maximal at multiplicities lower than 0.2 infectious particles/cell. The frequency of mutations resulting from cell pre-irradiation was only slightly higher for u.v.-irradiated than for intact virus. Thus, the induced cellular mutator appeared to be mostly untargeted in the dose range given to the virus. U.v.-irradiation of the cells also enhanced the mutagenesis of u.v.-irradiated herpes simplex virus, a double-stranded DNA virus ( Lytle and Knott , 1982).