The bovine papillomavirus type 1 E2 protein is a multifunctional early viral protein with roles in all phases of the cell cycle. E2 is required during G1 as a transcription factor, in S phase to initiate viral replication and during mitosis to tether the viral genome to dividing DNA. The viral genome contains 17 E2 binding sites, the majority of which are concentrated in the long control region (LCR), a regulatory region that is upstream of the viral coding sequence. The role of these binding sites has been explored in vitro using small plasmids and E1 and E2 proteins expressed in bacteria and insect cells. In this study we attempt to examine the placement of E2 on its binding sites during all phases of the cell cycle and in the context of a stably replicating viral system.

As part of the examination of the role of E2 during mitosis, we have also examined the role of the cohesin protein Scc1 in viral tethering. Two groups have published disparate reports identifying the cellular protein that binds to the transactivation domain of E2 to stably maintain viral genomes during cell division. Our group has published that it is the DNA helicase ChlR1 that is required for viral tethering, while it has been reported that it is the bromodomain protein Brd4 that is responsible. In this study we contribute to a report that shows that the cellular protein Scc1 binds to the viral genome through a ChlR1 independent mechanism. The cohesin protein binds to BPV-1 E2 at intermittent stages of the cell cycle and may be a factor in viral genome tethering. This interaction may also be important for regulating viral transcription.