It has been shown that purified SV40 large T antigen (Tag) forms a complex with both human and calf thymus DNA polymerase α and stimulates its activity. Furthermore, Tag has also been found to complex with purified human Rb protein. Here, we show the effect of Rb protein on the stimulation of DNA polymerase a by Tag, in an in vitro system using either purified human or calf thymus DNA polymerase a and either primed single-stranded M13 DNA or calf thymus-activated DNA. Both human and calf thymus enzymes were dose-dependently stimulated several fold by Tag. The stimulation was also observed in the coupled reaction of primase and polymerase α, using unprimed single-stranded M13 DNA. These stimulatory effects were, however, completely abolished by preincubating Tag with an equimolar amount of Rb protein. Primase activity of DNA polymerase α-primase complex was also stimulated by Tag, and this stimulation was abolished by the presence of Rb protein. In contrast, free primase was not affected by either Tag or Rb protein. Kinetic analysis revealed that in the presence of Tag the apparent Km for the template of either human or calf DNA polymerase a was decreased by approximately 2.5-fold and the V(max) was increased twofold, whereas Tag complexed with Rb protein did not affect the Km or the V(max) These results suggest a competition between Rb protein and DNA polymerase a for binding to Tag, which may be a key step for the initiation of SV40 DNA replication.
|Number of pages||7|
|Publication status||Published - 01-01-1993|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cancer Research