Role of the p68 subunit of human DNA polymerase alpha-primase in simian virus 40 DNA replication

Mol Cell Biol. 2002 Aug;22(16):5669-78. doi: 10.1128/MCB.22.16.5669-5678.2002.


DNA polymerase alpha-primase (pol-prim) is a heterotetramer with DNA polymerase and primase activities. The polymerase (p180) and primase (p48 and p58) subunits synthesize primers and extend them, but the function of the remaining subunit (p68) is poorly understood. Genetic studies in yeast suggested an essential role for the p68 ortholog in early S phase prior to the hydroxyurea-sensitive step, possibly a regulatory role in initiation of DNA replication, but found no evidence for an essential function of p68 later in S phase. To investigate whether the human p68 subunit has an essential role in DNA replication, we examined the ability of a purified trimeric human pol-prim lacking p68 to initiate simian virus 40 DNA replication in vitro and to synthesize and elongate primers on single-stranded DNA in the presence of T antigen and replication protein A (RPA). Both activities of trimeric pol-prim were defective, but activity was recovered upon addition of separately purified p68. Phosphorylation of p68 by cyclin A-dependent protein kinase also inhibited both activities of pol-prim. The data strongly suggest that the p68 subunit is required for priming activity of pol-prim in the presence of RPA and T antigen, both during initiation at the origin and during lagging strand replication.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens, Polyomavirus Transforming / metabolism
  • CDC2-CDC28 Kinases*
  • Cyclin A / metabolism
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases / metabolism
  • DNA Polymerase I / genetics
  • DNA Polymerase I / metabolism*
  • DNA Primase / genetics
  • DNA Primase / metabolism*
  • DNA Replication*
  • Humans
  • Macromolecular Substances
  • Phosphorylation
  • Protein Serine-Threonine Kinases / metabolism
  • Protein Structure, Quaternary
  • Protein Subunits
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Simian virus 40 / genetics*
  • Simian virus 40 / immunology
  • Simian virus 40 / physiology
  • Templates, Genetic
  • Virus Replication


  • Antigens, Polyomavirus Transforming
  • Cyclin A
  • Macromolecular Substances
  • Protein Subunits
  • Recombinant Proteins
  • Protein Serine-Threonine Kinases
  • CDC2-CDC28 Kinases
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases
  • DNA Primase
  • DNA polymerase alpha-primase
  • DNA Polymerase I