A transcriptional repressor encoded by BPV-1 shares a common carboxy-terminal domain with the E2 transactivator.

A negative-acting transcriptional regulatory factor encoded by bovine papillomavirus type 1 (BPV-1) was identified. This factor inhibits BPV-1-mediated transformation of mouse C127 cells; inhibition is BPV-1-specific and occurs only when the BPV-1 transforming genes are regulated by authentic transcriptional control elements. Plasmids expressing the inhibition function also repress E2 transactivation of the BPV-1 E2-dependent enhancer, and this repression is mediated by the same cis-acting element required for E2 transactivation. Inhibition of transformation may result from down-regulation of E2-dependent viral gene expression. Analysis of cDNA expressing the inhibition/repression activities mapped the function to the 3' domain of the E2 open reading frame. The E2 open reading frame thus encodes both positive and negative transcriptional regulatory factors, and these factors share a carboxy-terminal domain.