DNA helicase activity of SV40 large tumor antigen.

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Abstract
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.