Acidic transcription factors alleviate nucleosome-mediated repression of DNA replication of bovine papillomavirus type 1.

The papillomavirus E2 transcription factor is directly involved in viral DNA replication. Previous studies have shown that E2 interacts with both the viral E1 helicase and cellular replication proteins, and thus it may facilitate their targeting to the origin of replication. We demonstrate here that E1-mediated replication of bovine papillomavirus type 1 is repressed by nucleosomal assembly. The E2 protein counteracts this repression, and such activation requires the E2-binding sites adjacent to the origin of replication. These in vitro results are consistent with the previous in vivo findings that both E2 and specific E2 binding to DNA are absolutely required for replication of bovine papillomavirus. Furthermore, the function of E2 in preventing nucleosome-mediated repression can be achieved as well by several other acidic transcription factors. These data therefore strongly support the idea that a group of enhancer proteins may utilize similar mechanisms to stimulate transcription and replication.