Abstract
A ribonucleoprotein (RNP) particle sedimenting at 10 S in sucrose gradients had been isolated from the post-polysomal fraction of homogenates of 14-day-old chick embryonic leg and breast muscle by sucrose gradient fractionation and gel filtration. The 10 S RNP contains a 4 S RNA species (base composition: AMP, .3%; GMP, 22.2%; CMP, 24.2%; and UMP, 23.2%), and shows three major bands in the 70-90-nucleotide size range by polyacrylamide gel electrophoresis in 99% formamide. The 4 S RNA does not contain oligo(U)- and oligo(A)-rich tracts. The RNP has a characteristic buoyant density of 1.410 g/ml, which corresponds to an RNA/protein ratio of about 1:4. The UV absorption spectra of the RNP is very distinct from that of its RNA component. Both 4 S RNA and the 10 S RNP are potent inhibitors of translation of a variety of mRNAs such as chick muscle poly(A)+ mRNA, rabbit globin mRNA, EMC virus RNA, and poly(A)- and mRNA of rat liver in micrococcal nuclease-treated rabbit reticulocyte lysate. The inhibitory action of the RNA and the RNP on mRNA translation appears to involve the initiation process. The RNA and RNP do not have a nuclease activity associated with them. The hyperchromicity profile of the inhibitory RNA with increasing temperature indicates that it does not contain a significant amount of double-stranded structure. This is also supported by the complete loss of biological activity of the RNA by treatment with pancreatic RNase. In contrast, the inhibitory activity of the RNP was resistant to RNase. Electrophoresis of the protein moieties of the inhibitory RNP using both one- and two-dimensional gel techniques in the presence of sodium dodecyl sulfate shows a complex pattern of polypeptides of Mr = 12,000-150,000. The protein pattern of the 10 S particle is quite different from those of free and polysomal mRNP and poly(A)-protein complexes of chick embryonic muscles, indicating that most, if not all of the mRNA-associated proteins, are absent in the 19 S RNP. The properties of the inhibitory RNA indicate that it is different from the various low molecular weight RNA species which are involved in the modulation of protein synthesis in cell-free systems. It is concluded that the 10 S particle represents a novel class of RNP, which may be involved in posttranscriptional regulation of protein synthesis in embryonic muscles.
Highlights
A ribonucleoprotein (RNP) particle sedimenting at 10 S in sucrose gradients has been isolated from the postpolysomal fraction of homogenates of 14-day-old chick embryonic leg and breast muscle by sucrose gradient fractionation and gel filtration
The properties of the inhibitory RNA indicate that it is different from the various low molecular weight RNA species which are involved in the modulation of protein synthesis in cell-free systems
As part of our studies on translational control during muscle growth, we have looked for low molecular weight RNA species which may be involved in modulation of protein synthesis in chick embryonic muscles
Summary
The translation process during development [6]. The inhibitory RNA, Mr = 6,000, is pyrimidine-rich and is identical with tcRNA of chick embryonic muscles in base composition [6]. We have recently reported the isolation of a RNA species, from the 0.5 M KCl wash of chick embryonic muscle ribosomes, which is similar in size to tRNA and exhibits nonselective inhibitory action on in vitro mRNA translation [17, 18]. We describe the isolation and characterization of a cytoplasmic 10 S RNP particle containing an inhibitory RNA species in the 70-90-nucleotide size range from chick embryonic muscles. Both the 10 S particles (iRNP) and the deproteinized RNA moieties (iRNA) are found to be potent inhibitors of mRNA translation in vitro. Co.) it 1 or 6reactioo aitiurre conttaonintg10atMTris-HC1, pH7.2, 0mOfcKCI, ocMatmagnesiumaacetate at 30tCfor 3h
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have