YOLK GRANULES ARE THE MAJOR COMPARTMENT FOR BULLFROG (RANA-CATESBEIANA) OOCYTE-SPECIFIC RIBONUCLEASE

Rana catesbeiana ribonuclease (RC-RNase) is a pyrimidine guanine seque nce-specific ribonuclease found only in R. catesbeiana (bullfrog) oocy tes, not in other organs. An immunohistochemical assay showed that RC- RNase was present in the regular yolk granules, but not in forming yol k granules, yolk platelets, pigment granules, mitochondria clouds or t he nucleus. The RC-RNase was restricted to the lateral amorphous area of the yolk granules, and was absent from the central area that has a vitellogenin crystal lattice. The RC-RNase was extracted from yolk gra nules by 0.5 M NaCl and purified by dialysis and affinity chromatograp hy. Most of the RC-RNase (94%) was found in the yolk granules, the res t RC-RNase (6%) was found in the cytosol in the form of free RNase and latent RNase. The RC-RNase extracted from yolk granules was further a nalyzed by immunoprecipitation and RNase activity assay on an SDS/poly acrylamide gel. Our results suggest that the RC-RNase activity is regu lated by both compartmentation and inhibitor binding.