DNA helicase activity of SV40 large tumor antigen.
Large tumor antigen (T antigen) was extracted from SV40-infected African Green Monkey cells and purified to homogeneity by immunoaffinity chromatography. The purified T antigen preparations unwind DNA duplices of greater than 120 bp in a reaction which is dependent on magnesium ions and ATP hydrolysis. Based on these and other properties of the reaction we classify this newly discovered enzymatic activity as a eukaryotic DNA helicase. The helicase and the known ATPase function of T antigen cosediment with the mono- or dimeric 4-6 S form of T antigen, but not with higher T antigen aggregates. The helicase activity seems to be an intrinsic function of SV40 T antigen. First, several different T antigen-specific monoclonal antibodies interfere with the DNA unwinding activity; monoclonals which are known to reduce the T antigen-specific ATPase most strongly inhibited the helicase reaction. Second, mutant T antigens with impaired ATPase function also showed a reduced DNA unwinding activity.
D000818:Animals; D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D002522:Chlorocebus aethiops; D004264:DNA Topoisomerases, Type I / Q000302:isolation & purification / Q000378:metabolism*; D007668:Kidney; D007700:Kinetics; D009856:Oncogene Proteins, Viral / Q000302:isolation & purification / Q000378:metabolism*; D013539:Simian virus 40 / Q000201:enzymology*
D000952:Antigens, Polyomavirus Transforming; D000957:Antigens, Viral, Tumor; D009856:Oncogene Proteins, Viral; D004264:DNA Topoisomerases, Type I