Formation of mammalian preribosomes proceeds from intermediate to composed state during ribosome maturation.

摘要: In eukaryotes, ribosome assembly is a rate-limiting step in ribosomal biogenesis that takes place distinctive subnuclear organelle, the nucleolus. How ribosomes get assembled at nucleolar site by forming initial preribosomal complexes remains poorly characterized. this study, using several human and murine cell lines, we developed method for isolation of native mammalian lysing nuclei through mild sonication. A sucrose gradient fractionation nuclear lysate resolved ribonucleoprotein (RNP) containing rRNAs proteins. Characterization RNP with MS-based protein identification Northern blotting–based rRNA detection approaches identified two types preribosomes named here as intermediate (IPRibs) composed preribosome (CPRib). IPRib comprised large (105S to 125S size) modification factors premature rRNAs. We further observed CPRib complex consists an 85S mature factor, Ly1 antibody–reactive (LYAR), does not associate factors. rRNA-labeling experiments uncovered precedes formation. also found formation nutrient-dependent because abundances decreased substantially when cells were either deprived amino acids or exposed mTOR kinase inhibitor. These findings indicate form via dynamic processing events progress from state during maturation.