Domains of the BPV-1 E1 replication protein required for origin-specific DNA binding and interaction with the E2 transactivator.

The viral E1 and E2 proteins are required for replication of bovine papillomavirus type 1 DNA. Both proteins bind as a complex to the replication origin, which consists of an E1 binding site flanked on either side by E2 binding sites. The E1 protein has properties common to replication initiator proteins such as sequence-specific origin binding and DNA helicase activities. The E2 protein is a transcriptional transactivator that forms a complex with the E1 protein and enhances binding of E1 to the replication origin. We have mapped the regions of the E1 protein required for sequence-specific DNA binding, for cooperative binding with the E2 protein to the origin region, and for interaction with the E2 protein. These studies demonstrate that a region between amino acids 162 and 378 of the E1 protein is important for origin-specific DNA binding. The C-terminal half of the E1 protein is required in addition to the DNA binding domain (residues 162 to 605) for cooperative binding to the origin with the E2 protein. Binding studies confirmed that this region is also required for efficient complex formation with the E2 protein.