Abstract
Certain autoimmune sera contain antibodies against a nucleolar ribonucleoprotein particle associated with 7-2-RNA ( R. Reddy et al. (1983 ) J. Biol. Chem. 258, 1383; C. Hashimoto and J. A. Steitz (1983) J. Biol. Chem. 258, 1379). In this study, we showed by immunofluorescence microscopy that antibodies reactive with 7-2-ribonucleoprotein immunolocalized in the granular regions of actinomycin D and 5,6-dichloro-1-β- d-ribofuranosylbenzimidazole (DRB)—segregated nucleoli from Vero cells. By electron microscopic immunocytochemistry, antigen-antibody complexes were located in the granular component of transcriptionally active nucleoli from rat liver hepatocytes and HeLa cells. Anti-7-2-RNP antibodies from two autoimmune sera immunoprecipitated a major protein of M r 40,000 from [ 35S] methionine—labeled HeLa cell extract. The immunolocalization data suggest that 7-2-ribonucleoprotein may be involved in stages of ribosome biogenesis which take place in the granular component of the nucleolus, i.e., assembly, maturation, and/or transport of preribosomes.
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