The bovine papillomavirus origin of replication requires a binding site for the E2 transcriptional activator

The bovine papillomavirus type I transcriptional activator E2 is essential for replication of bovine papillomavirus DNA, yet most of the high-affinity binding sites for E2 are dispensable. Here we demonstrate an absolute requirement for a binding site for the E2 polypeptide as a cis-acting replication element, establishing that site-specific binding of E2 to the origin is a prerequisite for bovine papillomavirus replication in vivo. The position and distance of the E2 binding site relative to the other origin of replication components are flexible, but function at a distance requires high-affinity E2 binding sites. Thus, low-affinity binding sites function only when located close to the origin of replication, while activity at greater distances requires multimerized high-affinity E2 binding sites. The requirement for E2, although different in some respects, shows distinct similarities to what has been termed replication enhancers and may provide insight into the function of this class of DNA replication element.