THE 68-KILODALTON E1 PROTEIN OF BOVINE PAPILLOMAVIRUS IS A DNA-BINDING PHOSPHOPROTEIN WHICH ASSOCIATES WITH THE E2 TRANSCRIPTIONAL ACTIVATOR INVITRO

The E1 open reading frame of bovine papillomavirus type 1 encodes factors necessary for extrachromosomal maintenance of the viral genome in transformed cells. To facilitate biochemical characterization of the gene products encoded by this open reading frame, we have expressed the full-length E1 protein in a baculovirus-insect cell system. This protein was found to be phosphorylated and localized to the nucleus of infected cells. The E1 protein alone has affinity for DNA but appears to lack specificity for viral sequences. In addition, we present evidence that the E1 protein interacts with the virally encoded transcriptional activator E2 in vitro. These results are consistent with a model in which the E1 protein, as part of a complex with E2, interacts with specific DNA sequences in the viral genome.