The herpes simplex virus virion protein Vmw65 transcriptionally activates the gene encoding the U4 snRNA but not that encoding the U2 snRNA during lytic infection.

Although lytic infection with herpes simplex virus (HSV) causes the repression of most host cell biosynthesis, it results in increased transcription of the cellular gene encoding the U4 snRNA, leading to accumulation of this snRNA. In contrast, no increased transcription of the gene encoding the U2 snRNA or accumulation of this RNA is observed in infected cells. These effects are mediated by the HSV virion protein Vmw65, which activates the U4 gene but does not affect the U2 gene. The significance of this difference between the U2 and U4 genes is discussed with regard to the presence in both of these genes of an identical octamer-binding site for the cellular transcription factor Oct-1 which complexes with Vmw65.