Lagging strand synthesis in coordinated DNA synthesis by bacteriophage t7 replication proteins

J Mol Biol. 2002 Feb 8;316(1):19-34. doi: 10.1006/jmbi.2001.5325.


The proteins of bacteriophage T7 DNA replication mediate coordinated leading and lagging strand synthesis on a minicircle template. A distinguishing feature of the coordinated synthesis is the presence of a replication loop containing double and single-stranded DNA with a combined average length of 2600 nucleotides. Lagging strands consist of multiple Okazaki fragments, with an average length of 3000 nucleotides, suggesting that the replication loop dictates the frequency of initiation of Okazaki fragments. The size of Okazaki fragments is not affected by varying the components (T7 DNA polymerase, gene 4 helicase-primase, gene 2.5 single-stranded DNA binding protein, and rNTPs) of the reaction over a relatively wide range. Changes in the size of Okazaki fragments occurs only when leading and lagging strand synthesis is no longer coordinated. The synthesis of each Okazaki fragment is initiated by the synthesis of an RNA primer by the gene 4 primase at specific recognition sites. In the absence of a primase recognition site on the minicircle template no lagging strand synthesis occurs. The size of the Okazaki fragments is not affected by the number of recognition sites on the template.

Publication types

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

MeSH terms

  • Bacteriophage T7 / enzymology
  • Bacteriophage T7 / genetics*
  • Bacteriophage T7 / growth & development
  • Bacteriophage T7 / metabolism*
  • Base Composition
  • Base Sequence
  • Binding Sites
  • Cytidine Triphosphate / metabolism
  • DNA Primase / metabolism*
  • DNA Replication*
  • DNA, Single-Stranded / biosynthesis
  • DNA, Single-Stranded / genetics
  • DNA, Single-Stranded / metabolism
  • DNA, Viral / biosynthesis*
  • DNA, Viral / genetics
  • DNA, Viral / metabolism
  • DNA-Binding Proteins / metabolism*
  • DNA-Directed DNA Polymerase / metabolism*
  • Microscopy, Electron
  • Molecular Sequence Data
  • Substrate Specificity
  • Templates, Genetic


  • DNA, Single-Stranded
  • DNA, Viral
  • DNA-Binding Proteins
  • Cytidine Triphosphate
  • DNA Primase
  • bacteriophage T7 induced DNA polymerase
  • DNA-Directed DNA Polymerase