Is Dna Polymerase a Cytoplasmic Enzyme?

One of the most enigmat ic results of studies on the enzymic synthesis of D N A is tha t the polymerase is consistently found in homogena te fractions generally designated as cytoplasmic 0 4 ) . Since an unequivocal answer to the question of intracellular location of the enzyme seemed quite impossible from homogenate studies, we have taken a direct cytological approach to the problem. T he exper iment consists simply in in t roducing exogenous D N A 1 into living cells by means of pinocytosis in H3-thymidine medium. In the presence of the required enzymes ( thymidine kinase, thymidyla te kinase, and D N A polymerase) and the other substrates required for DNA synthesis, the ingested D N A serves as a pr imer for DNA synthesis. T he site of D N A synthesis is determined by autoradiographic detect ion of H 3thymidine incorporated into DNase-sensitive material . T he results suggest tha t D N A polymerase in Amoeba proteus may be present throughout the cytoplasm of non-dividing cells.