A new type of prosome-like particle, composed of small cytoplasmic RNA and multimers of a 21-kDa protein, inhibits protein synthesis in vitro.
A large fraction of the translationally repressed non-globin messenger RNA in duck erythroblasts is present in non-polyribosomal free mRNP structures which sediment in the 30-40-S range ('35 S'). In 0.5 M KCl, they form core complexes which show a pronounced peak at about 32 S containing mRNA and a discrete spherical RNP particle with a diameter of about 12 nm and the typical morphology of a prosome [H.-P. Schmid et al. (1984) EMBO J. 3, 29-34]. Buoyant density measurements and chromatography on oligo(dT)-cellulose indicate that this particle is bound to mRNA; it can be released from the mRNA by treatment of the free mRNP fraction with SDS. This prosome-like particle inhibits the translation of mRNA in vitro. It is composed primarily of multimers of a single 21-kDa protein and at least one species of RNA of about 80-100 nucleotides. It is resistant to dissociation by 2 M CS2SO4 and 1% SDS; the 21-kDa protein is not attacked by proteinase K unless the particle is extracted with phenol prior to treatment with the protease. The small RNA moiety of the particle hybridizes to the poly(A)-rich mRNA derived from the free mRNPs, as well as to polyribosomal mRNA. These data indicate that prosomes may serve to regulate mRNA translation; they show furthermore that prosome-like particles (about 600 kDa mass) may be built of up to 25 molecules of a single specific protein, rather than of the entire set of about 20 prosomal proteins previously identified.
Institut Jacques Monod, Paris, France.
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D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D004372:Ducks; D004900:Erythroblasts / Q000378:metabolism*; D005914:Globins / Q000235:genetics*; D007700:Kinetics; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008970:Molecular Weight; D009693:Nucleic Acid Hybridization; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics*; D012261:Ribonucleoproteins / Q000235:genetics* / Q000302:isolation & purification / Q000502:physiology
D046911:Macromolecular Substances; D012333:RNA, Messenger; D012261:Ribonucleoproteins; C026452:messenger ribonucleoprotein; D005914:Globins