Immunological localization of a major karyoskeletal protein in nucleoli of oocytes and somatic cells of Xenopus laevis.

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Abstract
Oocyte nuclei of X. laevis contain 2 major karyoskeletal proteins characterized by their resistance to extractions in high salt buffers and the detergent Triton X-100, i.e., a polypeptide of 68,000 MW which is located in the pore complex-lamina structure and a polypeptide of 145,000 MW enriched in nucleolar fractions. Both proteins are also different by tryptic peptide maps and immunological determinants. Mouse antibodies were raised against insoluble karyoskeletal proteins from Xenopus oocytes and analyzed by immunoblotting procedures. Affinity purified antibodies were prepared using antigens bound to nitrocellulose paper. In immunofluorescence microscopy of Xenopus oocytes purified antibodies against the polypeptide of 145,000 MW showed strong staining of nucleoli, with higher concentration in the nucleolar cortex and of smaller nucleoplasmic bodies. In various other cells including hepatocytes, Sertoli cells, spermatogonia and cultured kidney epithelial cells antibody staining was localized in small subnucleolar granules. The results support the conclusion that this insoluble protein is a major nucleus-specific protein which is specifically associated with, and characteristic of, nucleoli and certain nucleolus-related nuclear bodies. It represents the 1st case of a positive localization of a karyoskeletal protein in the nuclear interior, i.e., away from the pore complex-lamina structure of the nuclear cortex.

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