Immunological identification and localization of the predominant nuclear protein of the amphibian oocyte nucleus

Publisher Website
Google Scholar
Abstract
Nuclei of vitellogenic oocytes of the frog, X. laevis, contain a prominent protein, representing about 10% of nuclear protein, which is characterized by a polypeptide of MW 30,000. This protein is highly phosphorylated and acidic, displays several isoelectric variants with isoelectric point values ranging from 4.7-5.3, shows a high thermostability, is not stably complexed with other proteins and is readily extracted in buffer solutions. Guinea pig antibodies against this protein have allowed its specific immunoprecipitation and localization by immunofluorescence microscopy, using frozen tissue sections and cells grown in vitro. The protein is located almost exclusively in the nucleus where it appears to be spread throughout the nuclear interior. It is also a major nucleus-specific protein in vitellogenic and previtellogenic oocytes of other amphibian species as well as in other cell types, including hepatocytes, follicle epithelial cells and cultured Xenopus cells, but is not detected in nuclei of transcriptionally inactive cells such as erythrocytes and spermatids. An immunologically related, if not identical, protein occurs in nuclei of higher vertebrate cells, including mammals. The properties of this abundant nuclear phosphoprotein and its possible relationship to the nucleosome assembly factor protein are discussed. This soluble protein evidently serves a general nuclear function.