title: Simian virus 40 (SV40) DNA replication: SV40 large T antigen unwinds DNA containing the SV40 origin of replication.
abstract: The simian virus 40 (SV40) large T antigen (large tumor antigen), in conjunction with a topoisomerase, a DNA binding protein, and ATP, catalyzed the conversion of a circular duplex DNA molecule containing the SV40 origin of replication to a form with unusual electrophoretic mobility that we have named form U. Analysis of this molecule revealed it to be a highly underwound covalently closed circle. DNA unwinding was not detected with DNA containing a SV40 T-antigen binding site II mutation that renders the DNA inactive in replication. The unwinding reaction requires the action of a helicase, and SV40 T-antigen preparations contain such an activity. The T-antigen-associated ability to unwind DNA copurified with other activities intrinsic to T antigen [ability to support replication of SV40 DNA containing the SV40 origin, poly(dT)-stimulated ATPase activity, and DNA helicase]. However, in contrast to the unwinding activity, the SV40 T-antigen-associated helicase activity was not sequence-specific. A variety of labeled oligonucleotides hybridized with circular single-stranded DNA were displaced by T antigen in the presence of ATP.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000378:metabolism*; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004279:DNA, Viral / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells / Q000201:enzymology; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D010957:Plasmids; D013539:Simian virus 40 / Q000235:genetics*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D004279:DNA, Viral; D009856:Oncogene Proteins, Viral; D000251:Adenosine Triphosphatases; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II