A novel stimulating protein of mammalian DNA polymerase α

A DNA polymerase α-primase complex, which had been purified by means of immunoaffi-nity column chromatography, showed little activity in a reaction mixture composed of Tris-HCl buffer, but showed full activity in potassium phosphate buffer. It was found that potassium ion is required for the reaction by the immunoaffinity-purified enzyme. On the other hand, the DNA polymerase α purified by the orthodox biochemical method showed full activity in both buffer systems. A protein factor, which could restore the activity of immunoaffinity-purified DNA polymeraseα-primase complex in the potassium-free reaction mixture, was separated from biochemically purified DNA polymerase a. The factor, designated as factor T, was stable to heat up to 70°C, but was sensitive to trypsin. It sedimented at about 4S through a glycerol gradient. SDS-polyacrylamide gel electropho-resis revealed two polypeptide bands at 56 and 54 kDa. By immunoprecipitation, the factor T was shown to be physically associated with DNA polymerase α-primase complex. The stimulation was also observed with poly[d(A-T)], primed M13 DNA, and heat-denatured DNA.