Effects of T Antigen and Replication Protein a on the Initiation of DNA Synthesis by DNA Polymerase α-Primase

Kathleen L. Collins, Thomas J. Kelly

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153 Scopus citations


Studies of simian virus 40 (SV40) DNA replication in a reconstituted cell-free system have established that T antigen and two cellular replication proteins, replication protein A (RP-A) and DNA polymerase α-primase complex, are necessary and sufficient for initiation of DNA synthesis on duplex templates containing the SV40 origin of DNA replication. To better understand the mechanism of initiation of DNA synthesis, we analyzed the functional interactions of T antigen, RP-A, and DNA polymerase α-primase on model single-stranded DNA templates. Purified DNA polymerase α-primase was capable of initiating DNA synthesis de novo on unprimed single-stranded DNA templates. This reaction involved the synthesis of a short oligoribonucleotide primer which was then extended into a DNA chain. We observed that the synthesis of ribonucleotide primers by DNA polymerase α-primase is dramatically stimulated by SV40 T antigen. The presence of T antigen also increased the average length of the DNA product synthesized on primed and unprimed single-stranded DNA templates. These stimulatory effects of T antigen required direct contact with DNA polymerase α-primase complex and were most marked at low template and polymerase concentrations. We also observed tlat the single-stranded DNA binding protein, RP-A, strongly inhibits the primase activity of DNA polymerase α-primase, probably by blocking access of the enzyme to the template. T antigen partially reversed the inhibition caused by RP-A. Our data support a model in which DNA priming is mediated by a complex between T antigen and DNA polymerase α-primase. In this model, T antigen functions to facilitate the association of the DNA polymerase α-primase with the template, while RP-A acts to suppress nonspecific priming events.

Original languageEnglish (US)
Pages (from-to)2108-2115
Number of pages8
JournalMolecular and cellular biology
Issue number4
StatePublished - Apr 1991

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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