A complex between replication factor A (SSB) and DNA helicase stimulates DNA synthesis of DNA polymerase alpha on double-stranded DNA

FEBS Lett. 1992 Nov 9;312(2-3):143-6. doi: 10.1016/0014-5793(92)80922-4.


A helicase-like DNA unwinding activity was found in highly purified fractions of the calf thymus single-stranded DNA binding protein (ctSSB), also known as replication protein A (RP-A) or replication factor A (RF-A). This activity depended on the hydrolysis of ATP or dATP, and used CTP with a lower efficiency. ctSSB promoted the homologous DNA polymerase alpha to perform DNA synthesis on double-stranded templates containing replication fork-like structures. The rate and amount of DNA synthesis was found to be dependent on the concentration of ctSSB. At a 10-fold mass excess of ctSSB over double-stranded DNA, products of 200-600 nucleotides in length were obtained. This comprises or even exceeds the length of a eukaryotic Okazaki fragment. The ctSSB-associated DNA helicase activity is most likely a distinct protein rather than an inherent property of SSB, as inferred from titration experiments between SSB and DNA. The association of a helicase with SSB and the stimulatory action of this complex to the DNA polymerase alpha-catalyzed synthesis of double-stranded DNA suggests a cooperative function of the three enzymatic activities in the process of eukaryotic DNA replication.

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Animals
  • Base Sequence
  • Cattle
  • DNA / biosynthesis*
  • DNA Helicases / metabolism*
  • DNA Polymerase II / metabolism*
  • DNA Replication*
  • DNA-Binding Proteins / metabolism*
  • Molecular Sequence Data
  • Plasmids
  • Replication Protein A


  • DNA-Binding Proteins
  • Replication Protein A
  • Adenosine Triphosphate
  • DNA
  • DNA Polymerase II
  • DNA Helicases