Journal of Virology, December 1998, p. 9771-9781, Vol. 72, No. 12
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Institute for Molecular Biotechnology, 07745 Jena, Germany,1 and Department of Molecular Biology, Vanderbilt University, Nashville, Tennessee 37235, and Vanderbilt Cancer Center, Nashville, Tennessee 37232-68382
Received 6 July 1998/Accepted 4 September 1998
Physical interactions of simian virus 40 (SV40) large tumor (T)
antigen with cellular DNA polymerase
-primase (Pol/Prim) and
replication protein A (RPA) appear to be responsible for multiple functional interactions among these proteins that are required for
initiation of viral DNA replication at the origin, as well as
during lagging-strand synthesis. In this study, we mapped an RPA
binding site in T antigen (residues 164 to 249) that is embedded within
the DNA binding domain of T antigen. Two monoclonal antibodies whose
epitopes map within this region specifically interfered with RPA
binding to T antigen but did not affect T-antigen binding to
origin DNA or Pol/Prim, ATPase, or DNA helicase activity and had only a
modest effect on origin DNA unwinding, suggesting that they could be
used to test the functional importance of this RPA binding site in the
initiation of viral DNA replication. To rule out a possible effect of
these antibodies on origin DNA unwinding, we used a two-step initiation
reaction in which an underwound template was first generated in the
absence of primer synthesis. In the second step, primer synthesis was
monitored with or without the antibodies. Alternatively, an
underwound primed template was formed in the first step, and primer
elongation was tested with or without antibodies in the second step.
The results show that the antibodies specifically inhibited both primer
synthesis and primer elongation, demonstrating that this RPA binding
site in T antigen plays an essential role in both events.
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