The E2 open reading frame of BPV-1 encodes at least three proteins with transcriptional regulatory properties. The full-length E2 open reading frame encodes a transcriptional transactivator, and the 3' region encodes two polypeptides that repress E2-mediated transactivation. The full- length E2 gene product is also required in addition to the E1 protein for episomal viral DNA replication. A series of mutations were constructed within the E2 open reading frame and assayed for their ability to activate transcription and support viral DNA replication. This demonstrated that the replication and transactivation functions of the E2 protein are separable. The E1 and E2 proteins bind the replication origin as a complex. The laboratory is currently studying the role of E2 in viral DNA replication and determining which regions of the E2 protein are important for this interaction. The C-terminal domain of the E2 protein contains the specific DNA binding and dimerization properties of the protein but is not similar to other known DNA binding domains. Amino acid residues important for the DNA binding and dimerization properties have been identified by site-directed mutagenesis. Post-translational regulation of the E2 polypeptides by phosphorylation and by oxidation-reduction is also being analyzed.
