Expression of an immediate early polypeptide and activation of a viral origin of DNA replication in cells containing a fragment of herpes simplex virus DNA.

A thymidine kinase cotransformation procedure has been used to introduce the sequences encoding the herpes simplex virus type 1 (HSV-1) immediate early protein, Vmw175, into permissive cells either in the presence or the absence of the adjacent origin of viral DNA replication. Cells transformed by either origin-plus or origin-minus DNA were capable of expressing functional Vmw175 as indicated by their ability to complement the growth at the nonpermissive temperature of an HSV-1 mutant, ts K, containing a temperature-sensitive lesion in the Vmw175 gene. A proportion of the virus yield from cells transformed with the origin-plus, but not the origin-minus, plasmid exhibited a ts+ phenotype. The generation of ts+ virus correlated with an amplification of input plasmid DNA sequences which occurred following superinfection, suggesting that recombination between the ts mutant and the amplified viral DNA sequences had taken place. Encapsidation of the amplified DNA sequences was also detected, suggesting that in addition to a functional origin of replication and Vmw175 gene the transformed cells also retain the viral DNA packaging signals.