IMMUNOCYTOCHEMICAL LOCALIZATION OF RIBONUCLEASE IN YOLK GRANULES OF ADULT RANA-CATESBEIANA OOCYTES

To determine the localization of the pyrimidine-guanine sequence-speci fic ribonuclease in Rana catesbeiana (bullfrog) oocytes, the RNase was first isolated and used to prepare a specific rabbit antiserum. Only one protein of similar molecular size to the RNase was immunoprecipita ted from ovary homogenate by the antiserum, but two bands were observe d by Western blotting analysis. These two proteins were shown by furth er purification of antibody and Western blotting analysis to have simi lar antigenicity. Immunoprecipitation and Western blotting of tissue h omogenates showed that the RNase was found predominantly in the ovary, but not in other tissues. The specific localization of the RNase was determined by immune-electron microscopy of oocyte sections incubated with the specific antiserum; the yolk granules, but not other organell es, were found to contain the RNase. Most of the RNase was evenly dist ributed in the lateral amorphous area of the yolk granule but not in t he central yolk crystal area which contains stored vitellogenin protei ns. Our results indicate that the RNase is compartmentalized in the yo lk granules of oocytes, which might prevent damage to cellular RNAs.