YY1 is the cellular factor shown previously to bind to regulatory regions of several leaky-late (beta gamma, gamma 1) genes of herpes simplex virus type 1.

We have recently reported that a cellular factor, the leaky-late binding factor (LBF), binds to sites in a number of leaky-late (beta gamma or gamma 1) genes of herpes simplex virus type 1 and that an LBF site is essential for maximum viral transactivation of the major capsid protein (VP5) gene. The results of binding competition, partial proteolysis, and monoclonal antibody inhibition assays presented here establish that LBF is identical to the transcription factor YY1. This, along with our previous observations, suggests that YY1 plays a role in herpes simplex virus type 1 gene regulation.