title: Early nucleolar preribosomal RNA - protein in mammalian cells.
abstract: Early steps of ribosomal maturation have been studied by analysis of nucleolar extracts using different extraction procedures. Early 45-S nucleolar RNA is found to be associated with slowly sedimenting elements, distinct from previously described 80-S and 55-S nucleolar preribosomes. This early 45-S RNA has been shown to be of preribosomal type according to the following criteria. (a) When hybridized with nucleolar DNA, competition with rRNA can be observed; (b) its biosynthesis is sensitive to low doses of actinomycin D; (c) it is methylated at an early stage; (d) it contains no linked poly(A) segments. This early 45-S RNA seems to be specifically linked with proteins. The protein content of these early RNA-protein complexes is significantly lower than that for 80-S preribosomes. 45-S RNA sensitivity to nucleolytic activities that can take place in the course of preribosome extraction has been found to be higher in these RNA-protein complexes than in 80-S preribosomes. Identical results were obtained when different mammalian cell species were studied (rat, hamster, or HeLa cells).
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000032:analysis / Q000378:metabolism; D002458:Cell Fractionation; D002466:Cell Nucleolus / Q000032:analysis* / Q000378:metabolism; D005260:Female; D008113:Liver Neoplasms; D008433:Mathematics; D009374:Neoplasms, Experimental / Q000032:analysis / Q000378:metabolism; D009693:Nucleic Acid Hybridization; D014176:Protein Biosynthesis; D011506:Proteins / Q000032:analysis*; D012335:RNA, Ribosomal / Q000032:analysis* / Q000096:biosynthesis; D051381:Rats; D012270:Ribosomes / Q000378:metabolism
chemical_list: D011506:Proteins; D012335:RNA, Ribosomal