Ultraviolet-induced reactivation, amplification, and hypomethylation of a herpes simplex virus thymidine kinase gene.

A line of mouse cells containing a methylated inactive herpes simplex virus thymidine kinase (TK) gene was irradiated with ultraviolet (UV) light in an attempt to induce expression of the inactive TK gene. UV irradiation was shown to be capable of inducing expression of the viral TK gene in a dose-dependent manner. Analysis of the methylation pattern of the viral TK gene indicated that the active TK gene in three UV-induced TK+ cell line was methylated to a lesser extent than was the inactive viral TK gene in the parental cells. Analysis of the copy number of the viral TK gene in parental and UV-induced cell lines also revealed that the viral TK gene was amplified 3- to 20-fold in three of four UV-induced TK+ cell lines tested.