Studies on the role of the phi X174 gene A protein in phi X viral strand synthesis. II. Effects of DNA replication of mutations in the 30-nucleotide icosahedral bacteriophage origin

J Biol Chem. 1988 Nov 5;263(31):16433-42.


phi X174 viral strand circular DNA can be synthesized in vitro from phi X174 replicative form I (RFI) DNA in the presence of the phi X A protein, the Escherichia coli DNA polymerase III elongation system, the E. coli rep helicase, and the E. coli single-stranded DNA binding protein. M13mp9 or pBR322 RFI DNAs containing a 30-base pair sequence found at the phi X origin of replication supported phi X A protein synthesis as well as the phi X template, giving rise to a net molar excess of deoxynucleotide incorporation. In this paper, we show that mutations in positions 1-3 of the 30-nucleotide origin replicated at a lower efficiency than plasmids containing the wild-type origin, because of a deficiency in the reinitiation reaction. Mutations in positions 4-7, upstream of the phi X A protein cleavage site, failed to support replication because of their inability to support nicking. An origin containing a mutation at the residue to which the phi X A protein is covalently linked to the DNA was an active template that supported a net molar excess of incorporation. Mutations at the 3' end of the origin region, retaining only the first 21-25 nucleotides of the 30-base pair origin, failed to support replication because of impaired binding of the phi X A protein to the template and consequently poor nicking. A construct bearing the first 28 nucleotides of the origin supported wild-type replication, as did a plasmid containing a 28-mer origin with a point mutation at position 26, but this latter construct also appeared to be partially deficient in phi X A protein binding activity. These results are consistent with the presence of a phi X A protein binding domain at the 3' end of the origin.

Publication types

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

MeSH terms

  • Bacteriophage phi X 174 / genetics*
  • Base Sequence
  • DNA Replication*
  • DNA, Viral / genetics*
  • DNA, Viral / ultrastructure
  • Escherichia coli / genetics*
  • Kinetics
  • Molecular Sequence Data
  • Mutation*
  • Plasmids
  • Viral Proteins / physiology*


  • DNA, Viral
  • Viral Proteins