Cytoplasmic Location of DNA Polymerase in Oocytes of the Teleost Fish, Oryzias latipes

The intracellular location of DNA polymerase α during oocyte maturation in the teleost fish Oryzias latipes was examined. In order to define the optimum assay conditions, DNA polymerase α from the ovaries of the fish was isolated and partially purified by column chromatography before it was characterized. Optimum conditions for the assay of DNA polymerase α activity were Tris-HCl(pH7.8)as a buffer system and10-20mM Mg as a divalent cation when activated DNA was used as a template primer. In fully grown oocytes, almost all of the DNA polymerase α activity was found in enucleated oocytes but not in isolated germinal vesicles. In addition, analysis by isopycnic centrifugation showed that DNA polymerase α was associated with unknown membranes(probably, vesiculated endoplasmic reticulum)appeared in relatively low density fraction, but not with the endoplasmic reticulum in relatively high density fractions obtained from either immature or mature oocytes. These findings suggest that in oocytes of the fish DNA polymerase α exists in the cytoplasm in a different manner from that of the toad(Nagano et al.,1982). No qualitative change in DNA polymerase α activity was observed during the maturation process of the oocyte. However, the level of DNA polymerase α activity in mature oocytes was approximately2-fold that found in fully grown immature oocytes.