The transactivation and DNA binding domains of the BPV-1 E2 protein have different roles in cooperative origin binding with the E1 protein.

The bovine papillomavirus E2 transactivator protein enhances the ability of the E1 protein to bind to the viral origin of replication which contains an E1 binding site flanked by two E2 binding sites. To determine which regions and functions of the E2 protein are important for this cooperative interaction, a series of mutated E2 proteins were assayed for their ability to enhance E1 origin-specific binding. Cooperative origin binding required at least one E2 DNA binding site, an intact functional E2 DNA binding domain, and an intact transactivation domain. The hinge region of the E2 proteins was dispensable for this activity. To further examine the role of the E2 C-terminal domain, a series of chimeric proteins were generated that substituted the yeast GAL4 DNA binding domain for the E2 DNA binding domain. These chimeric proteins were able to cooperatively bind to a hybrid origin that contained GAL4 binding sites in place of the E2 binding sites. These studies indicate that the E2 transactivation domain is sufficient for interaction with the E1 protein and that the E2 DNA binding domain is required for interaction with origin DNA sequences.