A complex between replication factor A (SSB) and DNA helicase stimulates DNA synthesis of DNA polymerase alpha on double-stranded DNA.
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.
Zhang
S
S
German Primate Center, Department of Virology and Immunology, Göttingen.
Grosse
F
F
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D004247:DNA / Q000096:biosynthesis*; D004265:DNA Helicases / Q000378:metabolism*; D004257:DNA Polymerase II / Q000378:metabolism*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010957:Plasmids; D051716:Replication Protein A
D004268:DNA-Binding Proteins; D051716:Replication Protein A; D000255:Adenosine Triphosphate; D004247:DNA; D004257:DNA Polymerase II; D004265:DNA Helicases