SEGREGATION OF VIRAL PLASMIDS DEPENDS ON TETHERING TO CHROMOSOMES ANDIS REGULATED BY PHOSPHORYLATION

Eukaryotic viruses can maintain latency in dividing cells as extrachro mosomal nuclear plasmids, Segregation and nuclear retention of DNA is, therefore, a key issue in retaining copy number. The E2 enhancer prot ein of the papillomaviruses is required for viral DNA replication and transcription. Viral mutants that prevent phosphorylation of the bovin e papillomavirus type 1 (BPV) E2 protein are transformation-defective, despite normal viral gene expression and replication function. Cell c olonies harboring such mutants show sectoring of viral DNA and are una ble to maintain the episome, We find that transforming, viral DNA atta ches to mitotic chromosomes, in contrast to the mutant genome encoding the E2 phosphorylation mutant. Second-site suppressor mutations were uncovered in both E1 and E2 genes that allow for transformation, maint enance, and chromosomal attachment. E2 protein was also found to coloc alize to mitotic chromosomes, whereas the mutant did not, suggesting a direct role for E2 in viral attachment to chromosomes. Such viral hit ch-hiking onto cellular chromosomes is likely to provide a general mec hanism for maintaining nuclear plasmids.