Evidence for multiple vegetative DNA replication origins and alternative replication mechanisms of bovine papillomavirus type 1.

By following up the chance detection in the electron microscope of a DNA replication intermediate within a preparation of bovine papillomavirus (BPV-1) DNA isolated from purified virus particles, information was obtained about the mechanism of BPV-1 genome replication during the final stages of virus multiplication in naturally infected bovine wart tissue. The structure of viral replication intermediates was investigated by electron microscopic analysis of viral DNA linearized by digestion with restriction endonucleases which cleave the circular BPV-1 chromosome at defined sites. Both Cairns and rolling circle-type molecules were identified. Furthermore, replication eyes were widely distributed within the viral genome, indicating that vegetative BPV-1 DNA replication origins are largely uncoupled from previously described plasmid maintenance sequence elements.