The DNA polymerase α-DNA primase complex was purified over 17 000-fold to near homogeneity from calf thymus using an immunoaffinity column. Sodium dodecyl sulfate gel electrophoresis revealed three polypeptides with molecular weights of 140, 50 and 47 kDa, in a ratio of 1:2:0.25. The complex showed a sedimentation coefficient of 9.7 S, a Stokes radius of 56 Å and a native molecular weight of 250-260 kDa. Taken together, the data suggest that the calf thymus dNA polymerase α-DNA primase complex is essentially a heterotrimer of large (140 kDa) and small (50 kDa) subunits in a ratio of 1:2, with a globular conformation. Electron-microscopic studies of the complex revealed a spherical particle of 120 Å in diameter, in agreement with the physicochemical results. The binding of the complex to DNA was also demonstrated.
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