Disparate replication properties of integrated and extrachromosomal forms of bovine papilloma virus in ID13 cells.

Bovine papillomavirus (BPV) previously has been reported to exist in transformed rodent cell lines as both chromosomally integrated and extrachromosomal forms. In the BPV-transformed mouse cell line ID13, extrachromosomal BPV molecules replicate throughout S phase of the cell cycle in a random choice mode. We report here that these replication properties were altered for chromosomally integrated BPV DNA in five independent ID13 subclones. In all of the subclones, the integrated BPV sequences, which had no detectable deletions or mutations, existed in head-to-tail tandem arrays that replicated once per cell cycle, predominantly late in S phase. In contrast, extrachromosomal BPV molecules present in other subclones of the same cell line replicated in the random choice mode observed previously for non-integrated BPV. Our results indicate that the replication origin of integrated BPV either is inactivated as a consequence of chromosomal insertion, leading to the replication of BPV from origins in the flanking chromosomal DNA, or alternatively is reprogrammed to function in a once-per-cell cycle mode predominantly late in S phase.