Segregation of viral plasmids depends on tethering to chromosomes and is regulated by phosphorylation

Abstract

Eukaryotic viruses can maintain latency in dividing cells as extrachromosomal nuclear plasmids. Segregation and nuclear retention of DNA is, therefore, a key issue in retaining copy number. The E2 enhancer protein of the papillomaviruses is required for viral DNA replication and transcription. Viral mutants that prevent phosphorylation of the bovine papillomavirus type 1 (BPV) E2 protein are transformation-defective, despite normal viral gene expression and replication function. Cell colonies harboring such mutants show sectoring of viral DNA and are unable to maintain the episome. We find that transforming viral DNA attaches 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, maintenance, and chromosomal attachment. E2 protein was also found to colocalize to mitotic chromosomes, whereas the mutant did not, suggesting a direct role for E2 in viral attachment to chromosomes. Such viral hitch-hiking onto cellular chromosomes is likely to provide a general mechanism for maintaining nuclear plasmids.

Kaposi's sarcoma-associated herpesvirus LANA recruits the DNA polymerase clamp loader to mediate efficient replication and virus persistence

“…The observed virus loss with RFC deficiency suggests that these sites may be similarly sensitive to RFC deficiency, perhaps through LANA effects. Other episomal tumor viruses, including EBV, papillomaviruses, and polyomaviruses, may face similar needs to accelerate replication (40)(41)(42)(43). Whereas EBV nuclear antigen 1 interacts with ORCs and other licensing factors (44), Merkel cell polyomavirus (MCV) large T antigen recruits RFC to sites of MCV replication (45), suggesting that acceleration of PCNA loading may also occur with MCV.…”

Brd4 links chromatin targeting to HPV transcriptional silencing

“…Brd4 has recently been identified as the cellular adaptor mediating bovine papillomavirus type 1 (BPV-1) genome tethering to host mitotic chromosomes through its interaction with BPV-1 E2, thereby facilitating viral genome segregation during mitosis (You et al 2004). This genometethering function of BPV-1 E2 (Lehman and Botchan 1998;Skiadopoulos and McBride 1998;Ilves et al 1999) can be adapted for plasmid maintenance in Saccharomy-ces cerevisiae, provided that E2-binding sites are created in the plasmid and mammalian Brd4 is additionally introduced into yeast (Brannon et al 2005). The association between Brd4 and BPV-1 E2 with chromatin appears to be stable and persists through both mitosis and interphase (McPhillips et al 2005).…”

Maintenance of Epstein-Barr virus (EBV) oriP-based episomes requires EBV-encoded nuclear antigen-1 chromosome-binding domains, which can be replaced by high-mobility group-I or histone H1

“…Recently, bovine papillomavirus type 1 E2 protein has been found to have a chromosomeassociating domain that is critical for the maintenance of bovine papillomavirus type 1-derived episomes (42,43). The Kaposi sarcoma herpesvirus nuclear protein LANA also diffusely associates with mitotic chromosomes and mediates the long-term episome persistence of plasmids that include Kaposi sarcoma herpesvirus terminal-repeat DNA (44).…”