Persistent cytoplasmic location of a DNA polymerase β in sea urchins during development

Abstract

A subcellular localization study of a low molecular weight DNA polymerase β indicates that this enzyme, as well as a high molecular weight DNA polymerase α, is found in large quantities in the cytoplasm of Strongylocentrotus purpuratus eggs. The two enzyme activities are distinguished by DEAE-sievorptive chromatography and by their differential activities with activated DNA and oligo(dT) 10 · poly(dA) 200 primer-templates. Using an enucleation procedure, it is concluded that an extremely low proportion if any, of both polymerases is present in the egg nucleus. At blastula stage, a period of rapid cell proliferation, similar studies of DNA polymerase subcellular localization using two different methods of nuclear isolation indicate that the DNA polymerase β remains largely cytoplasmic while the α enzyme is found to be predominantly nuclear. Since the results for the α enzyme agree with previous reports (Loeb, L.A. (1969) J. Biol. Chem. 244, 1672) and since one method of nuclear isolation, using hypotonic solutions, enables us to recover both DNA polymerase α and β activities in isolated mouse L-cell nuclei, the enzyme quantitation of isolated sea urchin nuclei is considered accurate. Thus, although there is a translocation of the polymerase α from a cytoplasmic to nuclear site during early embryonic development, such a massive relocalization of the polymerase β does not occur.