Activation of herpes simplex virus 1 gamma 2 genes by viral DNA replication.

The expression of gamma 2 or true gamma genes resident in the herpes simplex virus 1 genome requires functional products of genes expressed earlier in infection and viral DNA synthesis. To determine whether the requirement for viral DNA synthesis for the expression of gamma 2 genes reflects a trans-acting function of a product of one or a few genes made or activated during viral DNA synthesis or whether it reflects a cis effect of DNA synthesis at specific sites, 143 thymidine kinase (TK) minus cells were sequentially infected with a virus carrying a 700-bp deletion of the TK gene and 6 hr later with wild-type or recombinant viruses carrying an alpha-TK or a gamma 2-TK gene in either the presence or absence of viral DNA synthesis. These experiments indicated that the gamma 2-TK gene contained in an unreplicated viral genome was not expressed by trans-acting factors specified before and during DNA synthesis by the first infecting virus, and, therefore, the induction of gamma 2 genes appears to be mediated by a cis-acting function associated with viral DNA synthesis.