title: Replication of viral DNA sequences integrated within the chromatin of SV40-transformed Chinese hamster lung cells.
abstract: To determine when during S phase integrated viral DNA sequences in several tsA SV40-transformed Chinese hamster cell clones replicate, we pulse-labeled cultures with BrdUrd and subsequently collected mitotic cells during sequential time intervals. Restriction endonuclease mapping indicated that each of the three SV40-transformed Chinese hamster lung cell clones contained a single viral DNA sequence at a different, but in each case unique, chromosomal site. DNA was extracted from each population of mitotic cells and then was resolved into dense, BrdUrd-containing and light, unsubstituted DNA fractions by cesium chloride gradient centrifugation. In each pair of samples obtained, we measured viral DNA sequences by solution hybridization using single-stranded SV40 32P-labeled DNA probes. Our results support the conclusions that specific genes within a mammalian DNA are programmed to replicate at particular times during S phase, and that the SV40 A gene product, large T antigen, programs integrated viral DNA sequences to replicate very early in S phase. The fractions of viral DNA replicated early in S phase appeared to correlate with each clone's content of functional large T antigen at permissive and nonpermissive culture temperatures.
mesh_terms: D000818:Animals; D002460:Cell Line; D002472:Cell Transformation, Viral; D006224:Cricetinae; D003412:Cricetulus; D004261:DNA Replication; D004279:DNA, Viral / Q000235:genetics*; D008168:Lung; D008242:Lysogeny; D013539:Simian virus 40 / Q000235:genetics*
chemical_list: D004279:DNA, Viral