IS DNA POLYMERASE A CYTOPLASMIC ENZYME?

Abstract

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 DNA<sup>1</sup> into living cells by means of pinocytosis in H<sup>3</sup>-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 H<sup>3</sup>- 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.