Isolation of low molecular weight RNAs from connective tissue. Inhibition of mRNA translation

Posttranscriptional control of embryonic rat skeletal muscle protein synthesis. Control at the level of translation by endogenous RNA

The onset of muscle cell differentiation is associated with increased transcription of muscle-specific mRNA. Studies from this laboratory using 19-d embryonic rat skeletal muscle, suggest that additional, posttranscriptional controls regulate maturation of muscle tissue via a quantitative effect upon translation, and that the regulatory component may reside within the poly A- RNA pool (Nathanson, M.A., E.W. Bush, and C. Vanderburg. 1986. J. Biol. Chem. 261:1477-1486). To further characterize muscle cell translational control, embryonic and adult total RNA were separated into oligo(dT)cellulose-bound (poly A+) and -unbound (poly A-) pools. Unbound material was subjected to agarose gel electrophoresis to resolve constituents of varying molecular size and mechanically cut into five fractions. Material of each fraction was electroeluted and recovered by precipitation. Equivalent loads of total RNA from 19-20-d embryonic rat skeletal muscle exhibited a 40% translational inhibition in comparison to its adult counterpart. Inhibition was not due to decreased message abundance because embryonic, as well as adult muscle, contained equivalent proportions of poly A+ mRNA. An inhibition assay, based upon the translatability of adult RNA and its inhibition by embryonic poly A- RNA, confirmed that inhibition was associated with a 160-2,000-nt poly A- fraction. Studies on the chemical composition of this fraction confirmed its RNA composition, the absence of ribonucleoprotein, and that its activity was absent from similarly fractionated adult RNA. Rescue of inhibition could be accomplished by addition of extra lysate or mRNA; however, smaller proportions of lysate were required, suggesting a strong interaction of inhibitor and components of the translational apparatus. Additional studies demonstrated that the inhibitor acted at the level of initiation, in a dose-dependent fashion. The present studies confirm the existence of translational control in skeletal muscle and suggest that it operates at the embryonic to adult transition. A model of muscle cell differentiation, based upon transcriptional control at the myoblast level, followed by translational regulation at the level of the postmitotic myoblast and/or myotube, is proposed.

Small nuclear ribonucleoprotein antigens are absent from 10S translation inhibitory ribonucleoprotein but present in cytoplasmic messenger ribonucleoprotein and polysomes

A cytoplasmic 10S ribonucleoprotein particle (iRNP), which is isolated from chick embryonic muscle, is a potent inhibitor of mRNA translation in vitro and contains a 4S translation inhibitory RNA species (iRNA). The iRNP particle shows similarity in size to the small nuclear ribonucleoprotein (snRNP) particles. Certain autoimmune disease patients contain antibodies directed against snRNP antigenic determinants. The possibility that iRNP may be related to the small nuclear particles was tested by immunoreactivity with monospecific autoimmune antibodies to six antigenic determinants (Sm, RNP, PM-1, SS-A (Ro), SS-B (La), and Scl-70). By Ouchterlony immunodiffusion assays, the cytoplasmic 10S iRNP did not show any immunoreactivity. Also, a more sensitive hemagglutination inhibition assay for detecting Sm and RNP antigens failed to show reactivity with the 10S iRNP. Thus, the 10S iRNP particles are distinct from the similarly sized snRNP. However, free and polysomal messenger ribonucleoprotein (mRNP) particles and polysomes also isolated from chick embryonic muscle and analyzed by Ouchterlony immunodiffusion and hemagglutination inhibition for the presence of the antigenic determinants showed reactivity to Sm and RNP autoantibodies, but were not antigenic for the other four antibodies. Some of the Sm antigenic peptides of mRNP particles and polysomes were identical to those purified from calf thymus nuclear extract, as judged by Western blot analysis. The association of Sm with free and polysomal mRNP and polysomes suggests that Sm may be involved in some cytoplasmic aspects of mRNA metabolism, in addition to a nuclear function in mRNA processing.

Generalized inhibition of cell-free translation by the amino-terminal propeptide of chick type I procollagen

Fragments of the amino-terminal propeptide of procollagen have been shown to inhibit the synthesis of procollagen in cultured cells and in a reticulocyte lysate cell-free system (for review see Timpl, R. and Glanville, R.W. (1981) Clin. Orth. Rel. Res. 158, 224-242). In this report, we show that the full-length amino-terminal propeptide of chick pro alpha1(I) chains inhibits the translation of chick tendon mRNA and rat brain mRNA in a reticulocyte lysate cell-free system. The synthesis of procollagen and non-collagenous proteins was equally affected. Inhibition was dose-dependent up to 10 microM. A similar pattern of inhibition was observed for the collagenase-resistant fragment, col 1(I).

Inhibition of cell-free protein synthesis by low-molecular-weight RNAs from free cytoplasmic ribonucleoprotein particles

Free cytoplasmic messenger ribonucleoprotein (mRNP) particles from rat liver were treated with EDTA and separated into two populations of RNP particles with sedimentation maxima of 20 S and 35 S respectively. The 20-S and 35-S RNP particles, treated with 0.5 M KCl, have protein-to-RNA ratios of 0.31:1 and 5.7:1 respectively. Whereas 20-S and 35-S RNP particles exhibit a similar protein complement of seven major polypeptides, the low-molecular-weight RNA components of the two particle populations are different. A characteristic set of distinct low-molecular-weight RNAs is found for 20-S and 35-S RNP particles. When the individual low-molecular-weight RNAs of 20-S and 35-S RNP particles isolated from preparative polyacrylamide gels were assayed for their capability to inhibit protein synthesis in vitro, several potent translational inhibitory RNAs were detected. In particular, the low-molecular-weight RNAs of 147, 203 and 263 nucleotides in length associated with the 35-S RNP particles turned out to be strong inhibitors of protein synthesis.

Nonselective inhibition of messenger RNA translation by highly purified low molecular weight RNA species from ribosomal salt wash of chick embryonic muscle

A low molecular weight RNA species, in the 70-90 nucleotide size range (iRNA), has been purified from the ribosomal salt wash of chick embryonic muscle by a combination of DEAE-cellulose and hydroxyapatite chromatography. This method yields iRNA free from contaminating tRNA and gives better and more reproducible yields than those obtained with our previous method involving lengthy dialysis of the salt wash. The iRNA at the concentration of 20-80 ng range strongly inhibits the translation of homologous and heterologous mRNAs i.e. chick muscle poly(A)+mRNA and rabbit globin mRNA; uncapped mRNA; and poly(A)-mRNA in micrococcal nuclease-treated reticulocyte lysate indicating that inhibition by iRNA is nonselective in nature. The translation of endogenous globin mRNA and polysomes in the lysate is strikingly less sensitive to iRNA suggesting that the initiation step is primarily affected by iRNA. The iRNA does not appear to be double-stranded RNA. It is concluded that iRNA is distinct from other low molecular weight RNA species described in the literature which modulate protein synthesis in cell-free systems.

The use of Taka-diastase in a[3H]poly(A) hybridization assay of oligo(U) sequences in RNA

A reliable assay of uridylate sequences longer than 10 is described. The procedure is based on the hybridization of [3H]poly(A) with poly(U) or oligo(U) sequences in high ionic conditions and a subsequent degradation of single stranded polynucleotides with purified Taka-diastase. A 1:2 complex between poly(A) and poly(U) is formed on which on poly(U) strand is digested by Taka-diastase. The procedure is especially suitable for the detection and quantitation of Un (n greater than 10) in RNA preparation.

Characterization of 20-S and 40-S non-polysomal cytoplasmic messenger ribonucleoprotein particles from rat liver

Two populations of free messenger ribonucleoprotein (mRNP) particles, sedimenting at 20 S and 40 S respectively, were isolated from a rat liver postpolysomal supernatant. After treatment with 0.5 M KCl and recentrifugation through a sucrose layer, the mRNP particles were characterized with respect to their low-molecular-weight RNA and protein components. 40-S and 20-S particles show very different RNA patterns. Four distinct low-molecular-weight RNA species of approximately 105, 139, 187 and 256 nucleotides were found as components of the 40-S mRNPs. The 20-S mRNP particles contain one major low-Mr RNA species of approximately 243 nucleotides and a characteristic pattern of low-Mr RNAs similar to the one found in nuclear ribonucleoprotein particles. In contrast to the low-Mr RNAs found in nuclear RNP particles most of the low-Mr RNA species present in 20-S and 40-S mRNP particles are rapidly labeled after [3H]orotate administration. Whereas the low-Mr RNA composition of 20-S and 40-S mRNP particles is very different, the protein patterns of both mRNP complexes are very similar. Six major polypeptides with the following molecular weights of 117000, 79800, 76700, 53800, 43900, 36300 and several minor ones were found in both 20-S and 40-S mRNPs. In a cell-free system from wheat germs neither 20-S nor 40-S mRNP particles stimulated the incorporation of [3H]leucine into proteins. However, phenol-extracted RNA from 20-S and 40-S mRNPs stimulated total protein synthesis 16-fold and 3-fold, respectively. Furthermore, the RNA from both mRNP pools directed the synthesis of albumin in vitro.

Oligo(U)- and poly(U)-containing RNA of wheat embryo

A UMP-rich RNA fraction was separated from the bulk cellular RNA by affinity chromatography of wheat embryo total RNA. The obtained preparation was heterogeneous and contained polyribonucleotide chain segments which were resistant to RNAase T1 and consisted mainly of UMP residues (87 mol%). The UMP-rich segments were of various sizes, including large oligonucleotides and polynucleotides (up to approx. 150 nucleotides in length). The oligo(U)- and poly(U)-containing RNA fraction occurred in a low amount (approx. 1% of total RNA) both in dry and germinating wheat embryos. However, at the onset of germination, labelled precursors were preferentially incorporated into the UMP-rich RNA species. The early-synthesized RNA appeared and underwent a considerable degradation within the cell nuclei. It is assumed that both delayed maturation of structural gene transcripts and rapid transcription of regulatory gene units during initial germination stages contribute to the transient abundance of newly made UMP-rich RNA in the early wheat embryos.

Myoblast stored myosin heavy chain transcripts are precursors to the myotube polysomal myosin heavy chain mRNAs

Radioactively labeled myosin heavy chain messenger ribonucleic acid (MHC mRNA) synthesized during the pre-fusion stage of chick embryo breast muscle cell culture is transferred from messenger ribonucleic acid proteins (mRNPs) to the polysomal MHC mRNA during the period of rapid increase in the rate of MHC synthesis (mid-to late-fusion). This transfer constitutes a major contribution to the rate of incorporation of 3H-labeled transcripts into polysomal MHC mRNA at this time. As the increase in the rate of MHC synthesis levels off (late-to post-fusion) the contribution to the rate of incorporation of 3H-labeled transcripts into polysomal MHC mRNA from newly synthesized transcripts increases until it becomes predominant. In vivo, the level of MHC mRNP increases during early stages of embryonic development and then decreases when MHC synthesis and the level of polysomal MHC mRNA has been shown to increase.

Extraction and translation of collagen mRNA from fetal calf skin

RNA was extracted from fetal calf skin by two different procedures, using phenol or guanidine hydrochloride. Poly(A)-rich RNA was separated by oligo(dT)-cellulose affinity chromatography and was further fractionated by sucrose density gradient centrifugation. When translated in an optimized wheat germ extract cell-free system, unfractionated guanidine-hydrochloride-extracted poly(A)-rich RNA directed the synthesis of two collagenase-sensitive protein bands, while phenol-extracted poly(A)-rich RNA with a sedimentation coefficient higher than 25 S was the only fraction to direct the same synthesis. On the basis of their electrophoretic mobility on a sodium dodecylsulfate/urea/polyacrylamide gel, these proteins were identified with procollagen alpha 1(I) and procollagen alpha 2. Inhibition of translation by phenol-extracted poly(A)-rich RNA with a sedimentation coefficient lower than 25 S was also observed. Guanidine-hydrochloride-extracted poly(A)-rich RNA from fetal skin directed the synthesis of three distinct collagenase-sensitive proteins in the micrococcal-nuclease-digested rabbit reticulocyte cell-free system; these seemed to correspond to procollagen alpha 1(I), procollagen alpha 2 and procollagen alpha 1 (III).

Low molecular weight RNAs as components of nuclear ribonucleoprotein particles containing heterogeneous nuclear RNA

70-130 S polyparticles as well as 38 S monoparticles were isolated from rat liver nuclei and analyzed in respect to their RNA components by microgel polyacrylamide electrophoresis in formamide. In addition to the high molecular weight polydisperse hnRNA of polyparticles several low molecular weight RNAs (snRNA) were detected. There are at least six distinct snRNA species in polyparticles. Except for one species, which is missing, 38 S monoparticles showed a similar snRNA pattern. From densitometer tracings of microgels the snRNAs were estimated to represent about 11% of the total polyparticle RNA. The number of nucleotides for the various snRNAs were determined from a plot of relative electrophoretic mobility versus log number of nucleotides. The possibility that the snRNAs are degradation products of the hnRNA was excluded on the basis of the following findings. (1) The snRNA pattern was similar in mono- and polyparticles. (2) Whereas the hnRNA of polyparticles incubated at 37 degrees C was extensively degraded, the snRNA did not show a corresponding increase. (3) After a 30 min pulse with [3H]orotate the hn RNA was readily labeled; none of the snRNAs, however, incorporated radioactivity. The snRNAs were still found after treatment of polyparticles with 2 M NaCl excluding contamination by nucleoplasm.