Is Dna Polymerase a Cytoplasmic Enzyme?

One of the most enigmatic results of studies on the enzymic synthesis of DNA is that the polymerase is consistently found in homogenate 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. The experiment consists simply in introducing exogenous DNA1 into living cells by means of pinocytosis in H3-thymidine medium. In the presence of the required enzymes (thymidine kinase, thymidylate kinase, and DNA polymerase) and the other substrates required for DNA synthesis, the ingested DNA serves as a primer for DNA synthesis. The site of DNA synthesis is determined by autoradiographic detection of H3- thymidine incorporated into DNase-sensitive material. The results suggest that DNA polymerase in Amoeba proteus may be present throughout the cytoplasm of non-dividing cells.