A complex of the bacteriophage T7 primase-helicase and DNA polymerase directs primer utilization

J Biol Chem. 2001 Jun 15;276(24):21809-20. doi: 10.1074/jbc.M101470200. Epub 2001 Mar 28.


The lagging strand of the replication fork is initially copied as short Okazaki fragments produced by the coupled activities of two template-dependent enzymes, a primase that synthesizes RNA primers and a DNA polymerase that elongates them. Gene 4 of bacteriophage T7 encodes a bifunctional primase-helicase that assembles into a ring-shaped hexamer with both DNA unwinding and primer synthesis activities. The primase is also required for the utilization of RNA primers by T7 DNA polymerase. It is not known how many subunits of the primase-helicase hexamer participate directly in the priming of DNA synthesis. In order to determine the minimal requirements for RNA primer utilization by T7 DNA polymerase, we created an altered gene 4 protein that does not form functional hexamers and consequently lacks detectable DNA unwinding activity. Remarkably, this monomeric primase readily primes DNA synthesis by T7 DNA polymerase on single-stranded templates. The monomeric gene 4 protein forms a specific and stable complex with T7 DNA polymerase and thereby delivers the RNA primer to the polymerase for the onset of DNA synthesis. These results show that a single subunit of the primase-helicase hexamer contains all of the residues required for primer synthesis and for utilization of primers by T7 DNA polymerase.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Bacteriophage T7 / enzymology*
  • Bacteriophage T7 / genetics
  • Base Pair Mismatch
  • Base Sequence
  • DNA Primase / chemistry*
  • DNA Primase / metabolism*
  • DNA Primers
  • DNA Replication
  • DNA, Viral / biosynthesis
  • DNA-Directed DNA Polymerase / chemistry
  • DNA-Directed DNA Polymerase / metabolism*
  • Kinetics
  • Models, Molecular
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Protein Structure, Secondary
  • Templates, Genetic


  • DNA Primers
  • DNA, Viral
  • Peptide Fragments
  • DNA Primase
  • DNA-Directed DNA Polymerase