Structural homology among calf thymus α-polymerase polypeptides

Abstract

A sample of highly purified calf thymus α-polymerase contained an abundant 118,000−M_r. polypeptide as well as five lower molecular weight polypeptides in the range of 54,000− to 64,000−M_r. This 118,000−M_r. polypeptide was capable of DNA polymerase activity, as revealed by in situ assay after SDS-polyacrylamide gel electrophoresis. Tryptic peptide mapping indicated that the 118,000−M_r polypeptide shared extensive primary structure homology with 57,000−, 58,000− and 64,000−M_r. polypeptides and some limited homology with 54,000− and 56,000−M_r polypeptides. This is the first evidence that lower and higher M_r polypeptides of purified calf thymus α-polymerase share sequence homology; these results are interpreted in the context of a model that predicts the existence of a common precursor with molecular weight >140,000.