Ultraviolet radiation induction of endogenous murine type C virus

Induction of endogenous type C RNA virus occurred following exposure of mouse cells to ultraviolet radiation. Irradiation of A1-2 cells, derived from the BALB/c mouse, induced endogenous xenotropic type C virus as determined by infectious center focus-forming assay on normal rat-kidney (NRK) cells. Viral induction by UV radiation was compared to that for the halogenated pyrimidines, 5-iodo-2-deoxyuridine (IdU) and 5-bromo-2-deoxyuridine (BrdU). Although the fraction of A1-2 cells induced to release virus by UV radiation (0.17%) was less than that observed for IdU (3.0%) and BrdU (0.46%), use of the sensitive infectious center assay demonstrated reproducible UV induction. Dose-response studies showed that the level of viral induction by UV was dependent upon cellular UV exposure. Study of A1-2 cell survival following irradiation showed that optimum viral induction occurred at a UV exposure corresponding to the edge of the shoulder of the survival curve, suggesting that UV sensitivity of the host cell may be a factor limiting the level of induction. Since less radiation was required for viral induction than for inactivation of colony-forming ability, viral induction may be a more sensitive dosimeter of in vitro UV bioeffects than cell survival for this system.