PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “RIBOSOMES”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 19 recordsLinked to original sources
PubMed1987

A comparison of accessibility of ribosomal proteins on free and membrane-bound ribosomes: the ribosomal proteins potentially involved in ribosome-membrane binding.

The relative accessibility of rat liver ribosomal proteins to reductive methylation was examined using membrane-bound and free ribosomes. Comparisons indicated that 12-13 large ribosomal proteins are masked by ribosomal association with membranes. These consisted of L8, L10, L17, L26-28, L31 and L36, and probably also include L4, L5, L7 and L29. These proteins seem to surround a region centered about L3 and may partly define a ribosomal channel through which the nascent peptide emerges. Approx. 10-20% of the large ribosomal subunit surface area is shielded by the membrane.

Animals↗
PubMed1978

Immunochemical analysis of the structure of eukaryotic ribosomes: antigenic properties of rat liver ribosomes and ribosomal proteins and characterization of the antisera.

Antibodies were prepared in rabbits and sheep to rat liver ribosomes, ribosomal subunits, and to mixtures of proteins from the particles. The antisera were characterized by quantitative immunoprecipitation, by passive hemagglutination, by immunodiffusion on Ouchterlony plates, and by immunoelectrophoresis. While all the antisera contained antibodies specific for ribosomal proteins, none had precipitating antibodies against ribosomal RNA. Rat liver ribosomal proteins were more immunogenic in sheep than rabbits, and the large ribosomal subunit and its proteins were more immunogenic than those of the 40S subparticle. Antisera specific for one or the other ribosomal subunit could be prepared; thus it is unlikely that there are antigenic determinants common to the proteins of the two subunits. When ribosomes, ribosomal subunits, or mixtures of proteins were used as antigens the sera contained antibodies directed against a large number of the ribosomal proteins.

Animals↗
PubMed1982

Influence of the state of ribosome association on the phosphorylation of ribosomal proteins in isolated ribosome--protein kinase systems from rat cerebral cortex.

Ribosomal protein phosphorylation was investigated in isolated ribosomal subunits and polyribosomes from rat cerebral cortex in the presence of [gamma-32P]ATP and purified catalytic subunit of cyclic AMP-dependent protein kinase from the same tissue. Ribosomal proteins that were most readily phosphorylated in isolated cerebral ribosomal subunits included proteins S2, S3a, S6 and S10 of the 40 S subunit and proteins L6, L13, L14, L19 and L29 of the 60 S subunit. These proteins were also phosphorylated in cellular preparations of rat cerebral cortex in situ or in vitro [Roberts & Ashby (1978) J. Biol. Chem. 253, 288-296; Roberts & Morelos (1979) Biochem. J. 184, 233-244]. However, several additional ribosomal proteins were phosphorylated when isolated 40 S or 60 S subunits were separately incubated in the reconstituted system. Analogous results were obtained with an equimolar mixture of cerebral 40 S and 60 S subunits under comparable conditions. In contrast, extensive exposure of purified cerebral polyribosomes to the catalytic subunit resulted in phosphorylation of only those ribosomal proteins of the 40 S subunit that were most highly labelled after the administration of [32P]Pi in vivo: proteins S2, S6 and S10. Ribosomal proteins of 60 S subunits that were readily phosphorylated in isolated cerebral polyribosomes included proteins L6, L13 and L29. These results indicate that polyribosome formation markedly decreases the number of ribosomal protein sites available for phosphorylation by the catalytic subunit of cyclic AMP-dependent protein kinase. Moreover, the findings suggest that, of the ribosomal protein phosphorylations observed in rat cerebral cortex in vivo, proteins S2, S6, S10, L6, L13 and L29 can be phosphorylated in polyribosomes, whereas proteins S3a, S5, L14 and L19 may become phosphorylated only in free ribosomal subunits.

Animals↗
PubMed1991

Ribosome binding to the endoplasmic reticulum: a 180-kD protein identified by crosslinking to membrane-bound ribosomes is not required for ribosome binding activity.

We have used the membrane-impermeable, thiol-cleavable, crosslinker 3,3'-dithio bis (sulfosuccinimidylpropionate) to identify proteins that are in the vicinity of membrane-bound ribosomes of the RER. A specific subset of RER proteins was reproducibly crosslinked to the ribosome. Immunoblot analysis of the crosslinked products with antibodies raised against signal recognition particle receptor, ribophorin I, and the 35-kD subunit of the signal sequence receptor demonstrated that these translocation components had been crosslinked to the ribosome, but each to a different extent. The most prominent polypeptide among the crosslinked products was a 180-kD protein that has recently been proposed to be a ribosome receptor (Savitz, A.J., and D.I. Meyer, 1990. Nature (Lond.). 346: 540-544). RER membrane proteins were reconstituted into liposomes and assayed with radiolabeled ribosomes to determine whether ribosome binding activity could be ascribed to the 180-kD protein. Differential detergent extraction was used to prepare soluble extracts of microsomal membrane vesicles that either contained or lacked the 180-kD protein. Liposomes reconstituted from both extracts bound ribosomes with essentially identical affinity. Additional fractionation experiments demonstrated that the bulk of the ribosome binding activity present in detergent extracts of microsomal membranes could be readily resolved from the 180-kD protein by size exclusion chromatography. Taken together, we conclude that the 180-kD protein is in the vicinity of membrane bound ribosomes, yet does not correspond to the ribosome receptor.

Animals↗
PubMed1984

Regulation of ribosome synthesis in Tetrahymena pyriformis. 1. Coordination of synthesis of ribosomal proteins and ribosomal RNA during nutritional shift-down.

When exponentially growing cells of Tetrahymena pyriformis are transferred to a non-nutrient medium the loss of whole cell RNA, 90% of which is ribosomal RNA, exhibits biphasic kinetics, whereas whole cell protein is lost at a constant rate. The ratio RNA/protein declines during the first 5 h of starvation and then remains constant during the subsequent period of starvation. The synthesis of the majority of the ribosomal proteins is coordinately regulated during a nutritional shift-down. Exponentially growing cells devote 17% of their capacity for protein synthesis to the production of ribosomal proteins. Upon starvation this proportion is rapidly reduced 3.5-fold. In long-time-starved cells the absolute rate of ribosomal protein synthesis is only about 4.5% of that of exponentially growing cells. The synthesis of ribosomal RNA and ribosomal proteins appears tightly coupled during the transition from growth to starvation. In long-time-starved cells the synthesis of ribosomal RNA and ribosomal proteins are stoichiometrically balanced with no significant degradation of de novo synthesized ribosomal proteins.

Animals↗
PubMed1976

The mitochondrial ribosomes of Neurospora crassa. II. Comparison of the proteins from Neurospora crassa mitochondrial ribosomes with ribosomal proteins from Neurospora cytoplasm, from rat liver mitochondria and from bacteria.

1. It has been shown by Datema et al. (Datema, R., Agsteribbe, E. and Kroon, A.M. (1974) Biochim. Biophys. Acta 335, 386--395) that Neurospora mitochondria isolated in a Mg2+-containing medium (or after homogenization of the mycelium in this medium and subsequent washing of the mitochondria in EDTA-containing medium) possess 80-S ribosomes; mitochondria homogenized and isolated in EDTA medium yield 73-S ribosomes. The ribosomal proteins of the subunits of 80-S and 73-S ribosomes were compared by two-dimensional electrophoresis. The protein patterns of the large, as well as of the small subunits are very similar but not completely identical; the most conspicuous difference is that the large subunit of 80 S contains about eight more proteins than the large subunit of 73 S. 2. The contamination by Neurospora cytoplasmic 77-S ribosomes in the 80-S preparations, if present, is only minor. 3. Neurospora cytoplasmic ribosomes contain 31 proteins in the large, and 21 proteins in the small subunit. 4. Neurospora 80- mitochondrial ribosomes contain 39 proteins in the large, and 30 proteins in the small subunit 30 proteins. 5. Rat liver mitochondrial ribosomes contain 40 proteins in the large and at least 30 proteins in the small subunit. About 50% of these proteins has an isoelectric point below pH 8.6. 6. The pattern of Paracoccus denitrificans is very similar to that of other bacterial ribosomes, the large subunit contains 29, the small subunit 18 proteins.

Animals↗
PubMed1991

Lack of complete cooperativity of ribosome assembly in vitro and its possible relevance to in vivo ribosome assembly and the regulation of ribosomal gene expression.

Earlier studies have shown that the reconstitution of Escherichia coli 50S as well as 30S ribosomal subunits from component rRNA and ribosomal protein (r-protein) molecules in vitro is not completely cooperative and binding of more than one r-protein to a single 16S rRNA (or 23S rRNA) molecule is required to initiate a successful 30S (or 50S) ribosome assembly reaction. We first confirmed this conclusion by carrying out 30S subunit reconstitution in the presence of a constant amount of 16S rRNA together with various amounts of total 30S r-proteins (TP30) and by analyzing the physical state of reconstituted particles rather than by assaying protein synthesizing activity of the particles as was done in the earlier studies. As expected, under conditions of excess rRNA, the efficiency of 30S subunit reconstitution per unit amount of TP30 decreased greatly with the decrease in the ratio of TP30 to rRNA, indicating the lack of complete cooperativity in the assembly reaction. We then asked the question whether the cooperativity of ribosome assembly is complete in vivo. We treated exponentially growing E coli cells with low concentrations of chloramphenicol which is known to inhibit protein synthesis without inhibiting rRNA synthesis, creating conditions of excess synthesis of rRNA relative to r-proteins. Several concentrations of chloramphenicol (ranging from 0.4 to 4.0 micrograms/ml) were used so that inhibition of protein synthesis ranged from 40 to 95%. Under these conditions, we examined the synthesis of RNA, ribosomal proteins and 50S ribosomal subunits as well as the synthesis of total protein. We found that the synthesis of 50S subunits was not inhibited as much as the synthesis of total protein at lower concentrations of chloramphenicol, but the degree of inhibition of 50S subunit synthesis increased sharply with increasing concentrations of chloramphenicol and was in fact greater than the degree of inhibition of total protein synthesis at chloramphenicol concentrations of 2 micrograms/ml or higher. The inhibition of 50S subunit synthesis was significantly greater than the inhibition of r-protein synthesis at all chloramphenicol concentrations examined. These data are consistent with the hypothesis that the cooperativity of ribosome assembly in vivo is also not complete as is the case for in vitro ribosome reconstitution, but are difficult, if not impossible, to explain on the basis of the complete cooperativity model.(ABSTRACT TRUNCATED AT 400 WORDS)

Centrifugation, Density Gradient↗
PubMed2004

Ribosome recycling factor disassembles the post-termination ribosomal complex independent of the ribosomal translocase activity of elongation factor G.

Ribosome recycling factor (RRF) disassembles post-termination ribosomal complexes in concert with elongation factor EF-G freeing the ribosome for a new round of polypeptide synthesis. How RRF interacts with EF-G and disassembles post-termination ribosomes is unknown. RRF is structurally similar to tRNA and is therefore thought to bind to the ribosomal A site and be translocated by EF-G during ribosome disassembly as a mimic of tRNA. However, EF-G variants that remain active in GTP hydrolysis but are defective in tRNA translocation fully activate RRF function in vivo and in vitro. Furthermore, RRF and the GTP form of EF-G do not co-occupy the terminating ribosome in vitro; RRF is ejected by EF-G from the preformed complex. These findings suggest that RRF is not a functional mimic of tRNA and disassembles the post-termination ribosomal complex independently of the translocation activity of EF-G.

Escherichia coli↗
PubMed1979

The polysomal proteins of L cells. Discrimination between the structural ribosomal proteins, the exchangeable ribosomal proteins and the non-ribosomal proteins by two-dimensional dodecylsulfate electrophoresis and autoradiography.

Three groups of proteins can be clearly discriminated in the total protein of L cell polysomes by selective labelling in the presence of low doses of actinomycin D and two-dimensional polyacrylamide/dodecylsulfate gel electrophoresis followed by autoradiography: (a) structural ribosomal proteins which are not labelled in the presence of actinomycin D and form stained non-radioactive spot in gels; (b) exchangeable ribosomal proteins which are labelled in the presence of actinomycin D and stained radioactive spots; (c) non-ribosomal proteins which are detectable only by autoradiography of gels. The large and small subunits of L cell ribosomes contain respectively 45 and 34 ribosomal proteins with molecular weights less than or equal to 50 000; seven of the large subunit proteins and nine of the small subunit proteins are exchangeable. Most of the non-ribosomal proteins migrate in the region of the related to the separation of the ribosomal proteins of mammalian cells and the possible significance of the presence of non-ribosomal proteins in polysomes are discussed.

Dactinomycin↗
PubMed1975

The ribosomal proteins of Drosophila melanogaster. V. Analysis by two-dimensional gel electrophoresis of the ribosomal proteins of the temperature-sensitive lethal allele of suppressor of forked, l(1) su(f)ts67g: a putative ribosomal protein mutant.

The possibility that the ribosomes of a temperature-sensitive lethal allele of suppressor of forked, l(1)su(f)ts67g, contain a mutated protein was studied by two-dimensional gel electrophoresis. The results from these analyses revealed no differences in the ribosomal proteins between the mutant and the wild-type strain Ks. It was found, however, that the transition from larval to adult ribosomal protein complement, which occurs mainly during the third instar in Käs, takes place during puparium formation in the mutant at 25 degrees C while it appears to be fatally delayed at 30 degrees C. Thus mutant larvae shifted up to 30 degrees C at 70 hours after oviposition failed to pupate, but reached the third instar and showed an adult ribosomal protein pattern after 4 days. Also, the ribosome content in these larvae was found to be significantly lower compared with late third instar larvae. It was furthermore found that larvae collected within 50 hours of transfer back to 25 degrees C, after a 5 day, 30 degrees C treatment, showed a reversion to a ribosomal protein pattern identical with that of Käs late third instar larvae. The results suggest that the biosynthesis of imaginal ribosomes in l(1)su(f)ts67g is seriously impaired at 30 degrees C and less so at 25 degrees C. Further studies are necessary, however, in order to understand the exact nature of this mutant, which may turn out to be a useful tool in studies on the biosynthesis of ribosomes in D. melanogaster.

Alleles↗
PubMed1962

The synthesis of ribosomes in E. coli. IV. The synthesis of ribosomal protein and the assembly of ribosomes.

The incorporation of C(14) leucine into the protein moiety of ribosomes has been studied as a sequel to the studies of ribosomal RNA synthesis. In contrast to the latter studies, labeled leucine is incorporated directly into 50S and 30S ribosomes without measurable delay by precursor stages. There is, however, evidence of some transfer of radioactivity from the 43S group of particles to the 50S. The inhibition of protein synthesis by chloramphenicol results in the accumulation of material similar to the eosome-the primary precursor in ribosome synthesis. There is also evidence for the synthesis of some neosome. The results of the studies of ribosomal RNA and protein synthesis are combined into a model of ribosome synthesis. Finally, consideration is made of the significance of these studies of ribosome synthesis for general problems of protein synthesis and information transfer.

Escherichia coli↗
PubMed2000

Extra-ribosomal function(s) of the plastid ribosomal protein L4 in the expression of ribosomal components in spinach.

We have previously characterised the cDNA corresponding to the nucleus-encoded, plastid ribosomal protein L4 from spinach. The L4 protein belongs to the group of ribosomal proteins for which extra-ribosomal functions have been demonstrated in prokaryotes. In general, these functions are concerned with the expression of ribosomal components. In order to analyse whether the plastid L4 protein might also have (an) extra-ribosomal function(s) we have produced the plastid L4 protein as a thioredoxin fusion protein and analysed its role in both prokaryotic (E. coli) and plastid systems. We found that the plastid L4 protein can replace the E. coli L4 protein in the NusA-dependent attenuation control of the E. coli S10 operon by stabilising stalled transcription complexes in a NusA-dependent reaction. In plastids, the L4 protein inhibits transcription of the rrn operon. Our results thus suggest extra-ribosomal function(s) for the plastid L4 protein in the expression of ribosomal components.

Amino Acid Sequence↗
PubMed1998

Directed hydroxyl radical probing of 16S ribosomal RNA in ribosomes containing Fe(II) tethered to ribosomal protein S20.

The 16S ribosomal RNA neighborhood of ribosomal protein S20 has been mapped, in both 30S subunits and 70S ribosomes, using directed hydroxyl radical probing. Cysteine residues were introduced at amino acid positions 14, 23, 49, and 57 of S20, and used for tethering 1-(p-bromoacetamidobenzyl)-Fe(II)-EDTA. In vitro reconstitution using Fe(II)-derivatized S20, together with the remaining small subunit ribosomal proteins and 16S ribosomal RNA (rRNA), yielded functional 30S subunits. Both 30S subunits and 70S ribosomes containing Fe(II)-S20 were purified and hydroxyl radicals were generated from the tethered Fe(II). Hydroxyl radical cleavage of the 16S rRNA backbone was monitored by primer extension. Different cleavage patterns in 16S rRNA were observed from Fe(II) tethered to each of the four positions, and these patterns were not significantly different in 30S and 70S ribosomes. Cleavage sites were mapped to positions 160-200, 320, and 340-350 in the 5' domain, and to positions 1427-1430 and 1439-1458 in the distal end of the penultimate stem of 16S rRNA, placing these regions near each other in three dimensions. These results are consistent with previous footprinting data that localized S20 near these 16S rRNA elements, providing evidence that S20, like S17, is located near the bottom of the 30S subunit.

Base Sequence↗
PubMed2002

Ribosomal and non-ribosomal resistance to oxazolidinones: species-specific idiosyncrasy of ribosomal alterations.

A derivative of Mycobacterium smegmatis, which carries only one functional rRNA (rrn) operon, was used to isolate mutants resistant to the ribosome-targeted antibiotic linezolid. Isolation and characterization of linezolid-resistant clones revealed two classes of mutants. Ribosomes from class I mutants are resistant to oxazolidinones in an in vitro peptidyl transferase assay, indicating that resistance maps to the ribosome component. In contrast, ribosomes from class II mutants show wild-type susceptibility to a linezolid derivative in vitro, pointing to a non-ribosomal mechanism of resistance. Introduction of a wild-type ribosomal RNA operon into linezolid-resistant strains restored linezolid sensitivity in class I mutants, indicating that resistance (i) maps to the rRNA and (ii) is recessive. Sequencing of the entire rrn operon identified a single nucleotide alteration in 23S rRNA of class I mutant strains, 2447G --> T (Escherichia coli numbering). Introduction of mutant rrl2447T into M. smegmatis rrn- resulted in a linezolid-resistant phenotype, demonstrating a cause-effect relationship of the 2447G --> T alteration. The 2447G --> T mutation, which renders M. smegmatis linezolid resistant, confers lethality in E. coli. This finding is strong evidence of structural and pos-sibly functional differences between the ribosomes of Gram-positive and Gram-negative bacteria. In agreement with the results of the in vitro assay, class II mutants show a wild-type sequence of the complete rRNA operon. The lack of cross-resistance of the class II mutants to other antibiotics suggests a resistance mechanism other than activation of a broad-spectrum multidrug transporter.

Acetamides↗
PubMed1989

Functional substitution of mouse ribosomal protein L27' for yeast ribosomal protein L29 in yeast ribosomes.

A cDNA clone of mouse ribosomal protein L27' was shown previously to be 62% identical in amino acid residues to yeast ribosomal protein L29. The L27' cDNA was expressed in yeast to determine the ability of the mouse protein to substitute for yeast L29 in assembling a functional ribosome. In a yeast strain resistant to cycloheximide by virtue of a recessive mutation in the L29 protein, the murine cDNA did not produce a sensitive phenotype, indicating failure of the mouse L27' protein to assemble into yeast ribosomes. However, when the mouse L27' gene was expressed in cells devoid of L29 and otherwise inviable, the murine protein supported normal growth, demonstrating that mouse ribosomal protein L27' indeed was interchangeable with yeast L29. We conclude that mouse ribosomal protein L27' is assembled into ribosomes in yeast, but yeast L29 is assembled preferentially when both L29 and L27' are present in the same cell.

Animals↗
PubMed1991

Monoclonal antibodies to Escherichia coli ribosomal proteins L9 and L10. Effects on ribosome function and localization of L9 on the surface of the 50 S ribosomal subunit.

Monoclonal antibodies against Escherichia coli ribosomal proteins L9 and L10 were obtained and their specificity confirmed by Western blot analysis of total ribosomal protein. This was particularly important for the L9 antibody, since the immunizing antigen mixture contained predominantly L11. Each antibody recognized both 70 S ribosomes and 50 S subunits. Affinity-purified antibodies were tested for their effect on in vitro assays of ribosome function. Anti-L10 and anti-L9 inhibited poly(U)-directed polyphenylalanine synthesis almost completely. The antibodies had no effect on subunit association or dissociation and neither antibody inhibited peptidyltransferase activity. Both antibodies inhibited the binding of the ternary complex that consisted of aminoacyl-tRNA, guanylyl beta, gamma-methylenediphosphonate, and elongation factor Tu, and the binding of elongation factor G to the ribosome. The intact antibodies were more potent inhibitors than the Fab fragments. In contrast to the previously established location of L10 at the base of the L7/L12 stalk near the factor-binding site, the site of anti-L9 binding to 50 S subunits was shown by immune electron microscopy to be on the L1 lateral protuberance opposite the L7/L12 stalk as viewed in the quasisymmetric projection. The inhibition of factor binding by both antibodies, although consistent with established properties of L10 in the ribosome, suggests a long range effect on subunit structure that is triggered by the binding of anti-L9.

Animals↗
PubMed1980

Ribosome-membrane interactions: characterization of ribosomal proteins from loose and tight bound ribosomes.

Membrane-bound ribosomes were isolated from a post-mitochondrial supernatant fraction of mouse liver homogenate by sedimentation in a sucrose density gradient, Loose ribosomes were released from the membrane fragments with 0.5 M KCl, while tight bound ribosomes were not released. After purification of the loose and tight ribosomes subclasses, ribosomal subunit proteins were isolated and compared by two-dimensional polyacrylamide gel electrophoresis. No differences in the ribosomal protein composition was detected.

Animals↗