Only one of the origin binding forms of SV40 T antigen has helicase activity.

SV40 T antigen exists in monomeric and multimeric forms. We have separated the individual components by glycerol gradient centrifugation. Helicase activity is found to be associated with monomeric forms only. Dimers and other multimeric forms have no discernable helicase activity. However, results obtained from DNA binding experiments carried out with separated forms of T antigen indicate that both monomers and dimers bind to region I and region II of SV40 origin of replication. Possibly monomeric T antigen unwinds DNA at the replication fork while both monomeric and dimeric forms are utilized for positioning of T antigen at the origin of replication.