Functional upstream activator sequences (TAATGARAT motifs) of herpes simplex virus immediate-early genes were identified and shown both to bind a factor (TRF) present in uninfected HeLa cells and to confer inducibility by the virus regulatory protein, Vmw65, on a normally nonresponsive promoter. Point-mutation analyses demonstrated binding specificity and correlated binding with Vmw65 induction. Furthermore, the octamer domains of the adenovirus DNA replication origin, the histone H2B, and the immunoglobulin light chain genes bound and competed for TRF. The immunoglobulin octamer also conferred Vmw65 inducibility on the TK promoter. In addition, a modified form of TRF was specifically detected in infected cells. We conclude that TRF is similar or identical to the previously described octamer binding protein and is likely to be the target for coordinate induction of immediate-early gene expression by Vmw65.