Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Polyribosomes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8Linked to original sources
PubMed1978

Acetylation of peptidyl-tRNA on rat liver polyribosomes.

Some properties of the known NH2-terminal acetylation of peptidyl-tRNA on rat liver polyribosomes were studied. Polyribosomes were incubated with [3H]acetyl-CoA and the products were separated into protein and peptidyl-tRNA fractions by an Ecteola-cellulose column procedure adapted for rapid, routine analysis of many samples, so that the characteristics of acetylation of the two fractions could be determined. Extraction of the polyribosomes with 0.5 MKC1--5mM Mg(OAc)2 solubilized acetyltransferase activity which could catalyze histone acetylation, and the extract when added back to the extracted could catalyze only a slight acetylation of peptidyl-tRNA free in solution isolated from polyribosomes by extraction with EDTA. These observations form the basis of any assay specific for the acetyl-CoA:peptidyl-tRNA N-acetyltransferase which is associated with rat liver polyribosomes.

Acetyl Coenzyme A↗
PubMed1976

Effect of tryptophan on hepatic polyribosomal disaggregation due to hypertonic sodium chloride.

The effect of tryptophan on the disaggregation of hepatic polyribosomes and on the inhibition of hepatic protein synthesis in rats due to the administration of hypertonic NaCl solutions was studied. Overnight-fasted rats were given by stomach tube or intraperitoneally hypertonic (6.2 to 10.7 per cent) NaCl alone or with 30 mg. of L-tryptophan and were killed 30 minutes later. The hypertonic NaCl treated rats revealed marked hepatic polyribosomal disaggregation and inhibition of hepatic protein synthesis (in vitro incorporation of 14C-leucine into proteins). Rats that received tryptophan alone or in a complete amino acid mixture in addition to hypertonic NaCl revealed a marked improvement in the patterns of hepatic polyribosomes and an increase in in vitro hepatic protein synthesis over that in hypertonic NaCl treated rats. The incorporation of 14C-orotate in hepatic messenger RNA (peak appearing between the 4 S and 18 S RNA fractions) associated with hepatic polyribosomes was studied. Administration of hypertonic NaCl alone caused a decrease in incorporation into hepatic messenger RNA whereas administration of hypertonic NaCl plus tryptophan caused an increase in incorporation into hepatic messenger RNA. Thus, tryptophan appears to cause an increase in hepatic messenger RNA as well as to prevent to a great extent the hepatic polyribosomal disaggregation and the inhibition of hepatic protein synthesis due to hypertonic NaCl.

Amino Acids↗
PubMedDate not supplied

[Interaction of eukaryotic aminoacyl-tRNA-synthases with polyribosomes].

Properties of rabbit liver tissue aminoacyl-tRNA synthetases, associated with polyribosomes, were studied under conditions of normal state and within 12 hrs after simulation of myocardium infarction. Under conditions of myocardium infarction the activity of some forms of aminoacyl-tRNA synthetase was decreased in polyribosomes and protein fractions, liberated from polyribosomes by means of washing with buffer containing 0.5 M KCl. Polyribosomes stimulated the synthetases and protected them from heat inactivation. Deterioration of the synthetases interaction with polyribosomes appears to be among the factors responsible for impairment of protein biosynthesis under conditions of myocardium infarction.

Amino Acyl-tRNA Synthetases↗
PubMed1988

[Functional and structural characteristics of polyribosomes associated with chick embryo cell nuclei].

Polyribosomes bound to the outer nuclear membrane was isolated from purified preparations of chicken embryo cell nuclei. These polyribosomes were shown to consist fractions forming unstable complexes with the nuclear membrane which can be separated from the latter by treatment with high ionic strength buffer solutions. Using sedimentation and gradient density analyses, the nuclei-bound RNP complexes were shown to be predominantly composed of 80S monosomes which take an active part in collagen polypeptide synthesis in cell-free protein-synthesizing systems. A comparison of sedimentation properties and collagen-synthesizing activity of nuclei-bound polyribosomes and cytoplasmic polyribosomes forming unstable complexes with endoplasmic membranes, it was concluded that the nuclei-bound 80S monosomes are an early step in the formation of cytoplasmic polyribosomes.

Animals↗
PubMed1985

[Free RNA-binding cytoplasmic proteins are detected in a labile association with polyribosomes].

A special fraction of RNA-binding proteins with a non-specific affinity for RNA is present in the extracts of eukaryotic cells. Earlier these proteins were considered exclusively as a pool of free informosomal proteins. It has been shown that a significant part (about 1/3) of RNA-binding proteins is found in labile association with mono- and polyribosome mass, respectively. The labile-associated proteins dissociate from the complex with mono- and polyribosomes with an increase in the ionic RNA-binding proteins bind to particles due to the non-specific affinity for the exposed part of RNA of mono- and polyribosomes. The decrease of the ionic strength leads to the stabilization of the RNA-binding proteins-polyribosomes complexes and enables purification of these complexes. A direct comparison by the O'Farrell two-dimensional analysis has shown that practically all the proteins that are labile-associated with polyribosomes are present within the preparation of free RNA-binding proteins.

Animals↗
PubMed1985

[Association of eukaryotic aminoacyl-tRNA-synthases with polyribosomes].

Upon fractionation of a mitochondria-free extract of rabbit reticulocytes into a ribosome-free extract and mono- and polyribosomes the bulk of the aminoacyl-tRNA synthetase activity was found in the fraction of mono- and polyribosomes. All the fifteen aminoacyl-tRNA synthetases were revealed, although in somewhat different quantities, in both fractions of the mitochondria-free reticulocyte extract. Aminoacyl-tRNA synthetases of the ribosome-free extract are found in two forms: RNA-binding one, and, the one having no affinity for high molecular weight RNAs. Aminoacyl-tRNA synthetases dissociated from the complexes with polyribosomes exist only in the RNA-binding form. All aminoacyl-tRNA synthetases can be removed from such complexes by an addition of 16S rRNA of E. coli, poly(U) or tRNA of rabbit reticulocytes. This testifies to labile association of aminoacyl-tRNA synthetases with the RNA-component of polyribosomes as well as to a rather nonspecific character of their interaction. After EDTA-induced dissociation of polyribosomes, the aminoacyl-tRNA synthetase activity was detected in the complex with both ribosomal subunits.

Amino Acyl-tRNA Synthetases↗
PubMed1978

[Effect of hydrocortisone on the properties of rat liver polyribosomes, metabolism, and template activity of polysomal poly-A-containing RNA].

The effect of hydrocortisone on the amount of newly synthesized polyribosomal poly-A+-RNA and its translation activity and the distribution of polyribosomes in the induction dynamics according to their size were studied. It was shown that 3-5 hours after intraperitoneal injection of hydrocortisone the incorporation of labelled precursors into polyribosomal poly-A+-mRNA is increased, which is accompanied by rapid accumulation of mRNA in the polyribosomes. Under prolonged induction those parameters come down to the initial level. 4-7 hours after the injection of the hormone the relative amount of heavy polyribosomes (350-412S) in liver cells is increased. It was found that hydrocortisone significantly changes the specific translation activity of polysomal poly-A+-mRNA: it shows an increase 2-4 hours after the hormone injection and returns to the initial level 12 hours after the injection.

Animals↗
PubMedDate not supplied

[Thyroglobulin biosynthesis and the content of thyroglobulin polyribosomes of the thyroid gland cells in the normal state and in various types of thyroid pathology].

The content of polyribosomes in human thyroid cells was studied in health and different forms of thyroid pathology. In thyroid pathology, thyroglobulin (TG) polyribosome content in thyroid cells diminished in the following order: diffuse toxic goiter greater than mixed euthyroid goiter greater than nodular toxic goiter greater than Hashimoto's goiter and complete absence of TG synthesizing polyribosomes in thyroid cancer and congenital goiter cells. No correlation was revealed between polyribosome TG content and thyroid function. It is inferred that impairment of TG biosynthesis in thyroid diseases is related to the decreased content of polyribosome TG in thyroid cells.

Humans↗
PubMed1980

[Biosynthesis of collagen in a cell-free system from wheat germ on poly(A)-RNA isolated from membrane-bound polyribosomes of chicken embryos].

The total protein-synthesizing and collagen-synthesizing activities of poly(A)-containing RNA from the membrane-bound polyribosomes of chicken embryos were studied under various conditions in a cell-free wheat germ system. The optimal concentrations of poly(A)-RNA, mono- and bivalent cations and spermine necessary for the translation of collagen and non-collagen proteins were determined. It was shown that within a wide range of K+ and Mg2+ concentrations in a cell-free system the poly(A)-RNAs studied are very actively involved in the translation of non-collagen proteins. At the same time the bacterial collagenase-cleavable polypeptides synthesized on poly(A)-RNA from the membrane-bound polyribosomes were identified only after addition of polyamine -- spermine (40 mk/M) to the system. In this case the relative level of collagen polypeptide synthesis remains constant within a wide range of concentrations of mRNA, K+ and Mg2+ in the system. Collagen-synthesizing activity of poly(A)-RNA from membrane-bound polyribosomes in a heterologous cell-free system as compared to that of membrane-bound polyribosomes in a homologous system showed that these polyribosomes can be effectively used for isolation of collagen mRNA.

Animals↗
PubMed1967

Regulation of polyribosome formation and protein synthesis in the uterus. Isolation of cytoplasmic ribonucleoprotein particles and the principal properties of the cell-free protein-synthesizing system.

1. Three procedures for isolating ribonucleoprotein particles from the cytoplasmic fraction of rat-uterus homogenates are described. By procedure 1, ribonucleoprotein particles were isolated in the presence of 5mm-Mg(2+) and 25mm-K(+), and the postmitochondrial supernatant fraction was made to 1.3% (w/v) in potassium deoxycholate. About 50% of the RNA and protein of the microsomal fraction was recovered in the monomeric ribosomes isolated. By procedure 2, ribonucleoprotein particles were isolated in the presence of 10mm-Mg(2+) and 0.1m-K(+), and in the absence of detergent. The ribosomes obtained were primarily polymeric, but recovery of microsomal RNA and protein was only 32%. By procedure 3, ribonucleoprotein particles were isolated according to procedure 1 but without the use of detergent. A mixture of polymeric and monomeric ribosomes was obtained, and the recovery of microsomal RNA and protein was about 60%. 2. Uterine polymeric and monomeric ribosomes, isolated by procedure 3 and designated ;polyribosomal preparation', were examined for protein-synthesizing capabilities. The principal properties of the cell-free protein-synthesizing system containing the polyribosomal preparation are described. The efficiency of amino acid incorporation in the complete system incubated for 30min. and containing the polyribosomal preparation was found to be either 2.5 molecules of [(14)C]leucine or 2.2 molecules of [(14)C]-valine incorporated/ribosome. Assay of the preparation in the complete cell-free system containing 10mm-sodium fluoride indicated that 40% of the incorporation activity is a result of initiation of new polypeptide chains and 60% is due to completion of previously existing chains. Monomeric ribosomes obtained by various treatments of the polyribosomal preparation with sodium fluoride, ribonuclease and potassium deoxycholate had decreased incorporation activity in the cell-free system. However, monomeric ribosomes obtained by treatment with sodium fluoride only had an incorporation activity 50% greater than that of monomers obtained by treatment with ribonuclease only. 3. The results indicate that uterine polymeric and monomeric ribosomes are sites of amino acid incorporation in vivo and in vitro. It is concluded that most polymeric and monomeric ribosomes occurring in the cytoplasmic fraction of the uterus are free and unattached to membranes, and that the polyribosomes are relatively unstable.

Journal Article↗
PubMed1970

Amino acid incorporation by ribosomes and polyribosomes from wheat chloroplasts.

Sucrose-gradient and analytical ultracentrifugation showed that chloroplast polyribosomes from 4-day-old seedlings had mono-, di-, tri-, tetra- and traces of penta-ribosomes, in contrast with those from 7-day-old seedlings in which only the mono-, di- and traces of tri-ribosomes were present. Without Mg(2+) the polyribosomes dissociated into ribosomal subunits. The rate of l-[U-(14)C]phenylalanine incorporation was threefold greater for preparations from 4- than from 7-day-old seedlings. Incorporation by the latter was stimulated by polyuridylic acid. The rates of incorporation were similar whether the reaction mixture contained chloroplast or wheat-germ transfer RNA and amino acid synthetases purified on methylated albumin-on-kieselguhr and Sephadex G-75 columns respectively. The cofactor requirement was the same as for isolated intact chloroplasts. Osmotic rupture of chloroplasts with and without Triton X-100 revealed the presence of free and bound ribosomes. Free single ribosomes isolated by osmotic shrinkage or prepared by pancreatic ribonuclease digestion of chloroplast polyribosomes had negligible incorporation activity. This activity was increased by washing or by polyuridylic acid, but was still only a fraction of that given by polyribosomes. A comparison of incorporation activity of chloroplast polyribosomes with those from the surrounding cytoplasm showed the former to be 20 times more active.

Amino Acids↗
PubMed1978

Isolation of polyribosomes and messenger RNA active in in vitro synthesis of soybean seed proteins.

Polyribosome preparations containing low proportions of monosomes to polyribosomes have been isolated from developing seeds of Glycine max L. Merrill using a high pH-high KCl buffer. The polyribosomes were functional in in vitro protein synthesis reactions using wheat germ 23,000g supernatant preparations. Results of experiments using aurintricarboxylic acid indicated that most or all of the amino acid incorporation in vitro resulted from the completion of nascent polypeptides associated with the isolated polyribosmes. RNA purified from polyribosome preparations by affinity chromatography on oligo(dT)-cellulose was also active in vitro, and had different Mg and K requirements for translation than did the polyribosomes. Translation of oligo(dT)-cellulose-purified mRNA was inhibited by the addition of 7-methylguanosine 5'-phosphate, suggesting that soybean mRNAs are "capped" at their 5' ends. Some, but not all, of the products of these reactions were identical in electrophoretic mobility to radioactive polypeptides of storage proteins produced in soybean cotyledons grown in culture.

Journal Article↗
PubMed1983

Restoration effects of glucose refeeding on reduced synthesis of albumin and total protein and on disaggregated polyribosomes in liver of starved rats: evidence of a post-transcriptional control mechanism.

Previous studies demonstrated that fasting is accompanied with a reduction of liver protein and albumin synthesis. A protein-deficient diet also leads to a marked change in liver RNA and protein metabolism. Although the reduction of protein synthesis and the disaggregated polyribosomes during fasting can be corrected by a single feeding of protein or a complete amino acid mixture, no or little changes of amino acid concentrations were found in portal blood and liver cytosol of fasted animals as compared to those of the fed group. To determine the effect of glucose on the reduced rate of protein and albumin synthesis of fasted rats, free and membrane-bound polyribosomes were isolated quantitatively from liver of starved rats (42-66 h) at different intervals after a single feeding of glucose and after giving glucose ad libitum for 24 h. (1) The yield of polyribosomal RNA decreased dramatically after a 42- to 66-hour starvation. A glucose refeeding did not change the RNA content. However, the restoration of polyribosome size could be observed rapidly. (2) At various levels of RNA, there was a decreased protein synthesis in fasted animals. However, the synthesis was enhanced after glucose refeeding. The albumin synthesis was also proportionately increased (10-12% of total protein synthesis of membrane-bound polyribosomes). (3) Glucose refeeding had no influence on the content of albumin mRNA sequence and liver RNA. These findings suggest that the effect of glucose on the restoration of protein and albumin synthesis is a sole post-transcriptional event.

Albumins↗
PubMed1977

The in vivo effect of dimethyl sulphoxide (DMSO) on protein synthesis and the polyribosome profile in Paramecium.

When Paramecium tetraurelia in log phase growth is treated with 4% dimethyl sulphoxide (DMSO) for five minutes the amount of polyribosomes is reduced 3- to 4-fold while there is a corresponding increase in 80s ribosomal material. Reducing the concentration of DMSO to 1% allows immediate reversal of the condition. Paramecium polyribosomes subjected to 4% DMSO either in whole cell homogenates or during purification through sucrose density gradients appear unaffected while cycloheximide at concentrations up to 100 mug/ml did not prevent DMSO from exerting its effect in vivo. Analyses of 14C amino acid incorporation experiments indicated a strict correspondence between the effect of DMSO on polyribosomes and overall protein synthesis. The reduction of acid precipitable radioactivity in the polyribosomal region after DMSO treatment was associated with a corresponding increase in radioactivity in the 80s region. There was no comparable increase in the acid precipitable radioactivity in the soluble fraction. The overall results of the study suggest that DMSO acts on polyribosommes indirectly through some unknown primary reaction with cell constitutents, and that the mode of action is such as to cause the release of ribosomes from messenger RNA (mRNA) rather than to prevent initiation of the ribosome-mRNA complex. Our data suggest that the effect may be selective. Finally, it is of interest that high concentrations of DMSO (above 8%) appear to have the opposite effect of lower concentrations of DMSO, i.e., they appear to "freeze" the ribosomes to mRNA.

Animals↗
PubMed1996

Polyribosome dynamics: size-distribution as a function of attachment, translocation and release of ribosomes.

Assembly of polyribosomes is the ubiquitous manifestation of the activation of translational machinery in cells. This is accompanied by a concomitant appearance of mRNAs either from an activation of pre-existing ribo-nucleoprotein particles (RNP) or from newly synthesized transcripts. The size-distributions of polyribosomes as inferred from their sedimentation profiles are essentially defined by various kinetic parameters responsible for continuous flux of ribosomes due to their recycling between the "free" and the "bound" states. In the theoretical analysis presented here the time-evolution of polyribosomes and their sustenance in the steady state is considered as a Markovian process with the states of mRNAs defined as the number of ribosomes attached. Expressions for the elements of one-step transition matrix as a function of kinetic parameters related to the initiation, translocation and the release of ribosomes and the size of mRNA are derived. The latter is shown to be relevant only in so far as it sets an upper limit to the size of polyribosomes. Implications of transient arrest of ribosomes at the initiation site as envisaged in the signal hypothesis for the synthesis of secretory proteins and the putative role of receptor-mediated post-translational transport of proteins have been examined. Results of computer simulations on model systems have focussed attention on the diverse types of profiles that may appear under varying physiological conditions.

Animals↗
PubMed1990

Combined use of oligo(dt) and 28S cDNA probes for the quantitation of total mRNA in polyribosomes: application to the castration-induced atrophy of the rat prostate.

The castration-induced atrophy of the rat prostate was used as a model for the validation of a sensitive technique allowing the quantitation of total mRNA in polyribosomes. Electron micrographs of polyribosome samples showed a decrease in polyribosomes length 7 days after castration (GDX). Specificity of labeled oligo(dt) probe for poly(A) was demonstrated and the technique was successfully applied to demonstrate that GDX is associated with a decrease in poly(A) mRNA content of polyribosomes. Provided that normalization of the hybridization signal for mRNA is achieved with a rRNA cDNA probe, the assay therefore represents a suitable tool for further studies regarding the translational regulation of total and/or specific mRNAs.

Animals↗
PubMed1986

Synthesis of large subunit of ribulosebisphosphate carboxylase by thylakoid-bound polyribosomes from spinach chloroplasts.

Intact chloroplasts were isolated from developing first leaves of spinach. The chloroplasts were broken and separated into an extensively washed membrane (thylakoid) fraction and a soluble (stroma) fraction. The membrane fraction contained polyribosomes with properties similar to those of thylakoid-bound polyribosomes of other organisms. The distribution of mRNA for large-subunit ribulosebisphosphate carboxylase (LS) was determined by translating RNA from chloroplasts, thylakoids, and stroma in a wheat germ cell-free translation system. LS translation product was identified by immunoprecipitation with antibody to LS from spinach, electrophoresis of the immunoprecipitated product, and fluorography. At least 44% of translatable chloroplast LS-mRNA was in the washed thylakoid fraction. Thylakoid-bound LS-mRNA was in polyribosomes since LS was produced by thylakoids in an Escherichia coli cell-free translation system under conditions where initiation did not take place. Our results demonstrate that membrane-bound polyribosomes can synthesize the stroma-localized polypeptide LS, and suggest that the thylakoids may be an important site of its synthesis.

Chemical Precipitation↗
PubMed1974

Informational ribonucleoprotein particles of newt oocytes: polyribosome-associated ribonucleoproteins.

Various species of rapidly labelled, informational ribonucleoproteins can be isolated from homogenates of newt oocytes. Polyribosome-associated ribonucleoprotein can be separated from heterogeneous nuclear ribonucleoprotein and free cytoplasmic ribonucleoprotein by sucrose gradient centrifugation. The polyribosome-associated ribonucleoprotein can be released from the ribosome complex by treatment with low concentrations of EDTA and has the following properties: 1. It is rapidly labelled with [3H]uridine under condition (incubation of oocytes for 4 h and less at 20 degrees C) where there is no detectable labelling of ribosomal subunits. 2. It is heterogeneous in size, consisting of particles most of which sediment between 40 S and 80 S. 3. Its sedimentation coefficient is related directly to the size of the polyribosomal complex from which it is derived. 4. Its density ranges from 1.35 g/cm3 to 1.55 g/cm3 irrespective of size. This indicates protein to RNA ratios of 4:1 to 2:1. 5. It is active, when complexed with ribosomes, in cell-free protein synthesis. It is concluded that this polyribosome-associated ribonucleoprotein is functional messenger and its role in oocyte maturation is discussed.

Animals↗