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At least 127 records · Page 7Linked to original sources
PubMed1997

Release factor RF3 abolishes competition between release factor RF1 and ribosome recycling factor (RRF) for a ribosome binding site.

The dependence of the rate of ribosomal recycling (from initiation via protein elongation and termination, and then back to initiation) on the concentrations of release factor RF1 and the ribosome recycling factor (RRF) has been studied in vitro. High RF1 concentration was found to reduce the rate of ribosomal recycling and the extent of this reduction depended on stop codon context. The inhibitory effect of high RF1 concentrations can be reversed by a corresponding increase in RRF concentration. This indicates that RF1 and RRF have mutually exclusive and perhaps overlapping binding sites on the ribosome. Addition of release factor RF3 to the translation system abolishes the inhibitory effect of high RF1 concentration and increases the overall rate of ribosome recycling. These data can be explained by a three-step model for termination where the first step is RF1-promoted hydrolysis of peptidyl-tRNA. The second step is an intrinsically slow dissociation of RF1 which is accelerated by RF3. The third step, catalysed by RRF and elongation factor G, leads to mobility of the ribosome on mRNA allowing it to enter a further round of translation. In the absence of RF3, RF1 can re-associate rapidly with the ribosome after peptidyl-tRNA hydrolysis, preventing RRF from entering the ribosomal A-site and thereby inhibiting ribosomal recycling. The overproduction of RF1 in cells deficient in RRF or lacking RF3 has effects on growth rate predicted by the in vitro experiments.

Bacterial Proteins↗
PubMed1977

In vivo incorporation of ribosomal proteins into HeLa cell ribosomal particles.

Using high salt-washed ribosomal subunits from HeLa cells we detect three ribosomal proteins from the small subunit and five ribosomal proteins from the large subunit that enter ribosomal particles in the absence of ribosome formation (actinomycin D-treated cells); in untreated cells, they enter the ribosomal particles quickly, while the rest of the ribosomal proteins are incorporated gradually. At least two of the large subunit actinomycin D-resistant ribosomal proteins seem to be absent in the 55 S nucleolar ribosomal precursor.

Carbon Radioisotopes↗
PubMed2002

Positioning of the mRNA stop signal with respect to polypeptide chain release factors and ribosomal proteins in 80S ribosomes.

To study positioning of the mRNA stop signal with respect to polypeptide chain release factors (RFs) and ribosomal components within human 80S ribosomes, photoreactive mRNA analogs were applied. Derivatives of the UUCUAAA heptaribonucleotide containing the UUC codon for Phe and the stop signal UAAA, which bore a perfluoroaryl azido group at either the fourth nucleotide or the 3'-terminal phosphate, were synthesized. The UUC codon was directed to the ribosomal P site by the cognate tRNA(Phe), targeting the UAA stop codon to the A site. Mild UV irradiation of the ternary complexes consisting of the 80S ribosome, the mRNA analog and tRNA resulted in tRNA-dependent crosslinking of the mRNA analogs to the 40S ribosomal proteins and the 18S rRNA. mRNA analogs with the photoreactive group at the fourth uridine (the first base of the stop codon) crosslinked mainly to protein S15 (and much less to S2). For the 3'-modified mRNA analog, the major crosslinking target was protein S2, while protein S15 was much less crosslinked. Crosslinking of eukaryotic (e) RF1 was entirely dependent on the presence of a stop signal in the mRNA analog. eRF3 in the presence of eRF1 did not crosslink, but decreased the yield of eRF1 crosslinking. We conclude that (i) proteins S15 and S2 of the 40S ribosomal subunit are located near the A site-bound codon; (ii) eRF1 can induce spatial rearrangement of the 80S ribosome leading to movement of protein L4 of the 60S ribosomal subunit closer to the codon located at the A site; (iii) within the 80S ribosome, eRF3 in the presence of eRF1 does not contact the stop codon at the A site and is probably located mostly (if not entirely) on the 60S subunit.

Codon, Terminator↗
PubMed1974

Mitochondrial and cytoplasmic ribosomes. Distinguishing characteristics and a requirement for the homologous ribosomal salt-extractable fraction for protein synthesis.

1. Mitochondrial and cytoplasmic ribosomes of Euglena gracilis differ in their total RNA and protein content. 2. Mitochondrial ribosomes dissociate to subunits at higher Mg(2+) concentrations than do cytoplasmic ribosomes. 3. A separable 5S RNA is obtained from cytoplasmic and chloroplast ribosomes, but not from mitochondrial ribosomes. 4. For protein-synthesizing activity with a natural mRNA, mitochondrial ribosomes use tRNA from any cell compartment and are partly active with supernatant enzymes from cytoplasm. Cytoplasmic ribosomes are partly active with enzymes and tRNA from mitochondria or chloroplasts. 5. Both mitochondrial and cytoplasmic ribosomes show high specificity for the homologous salt-extractable ribosomal fraction for protein-synthesizing activity.

Cell Fractionation↗
PubMed1976

Radioactive labelling of ribosomal proteins with reductive alkylation and its use in studying ribosome-cytosol interactions.

Mouse brain ribosomes were radioactively labelled by a cell-free reductive alkylation reaction with NaBH4 and [14C]formaldehyde. The radioactivity was largely associated with ribosomal proteins, but little, if any, of the rRNA was radioactive after the alkylation procedure. Both ribosomal structural proteins and loosely associated components were successfully labelled by this procedure. The sedimentation properties of the ribosomes were unaltered and their ability to carry out poly(U)-directed protein synthesis, although decreased, was largely retained. Incubation of 14C-labelled ribosomes with brain cytosol resulted in a 17% loss of radioactivity, although treatment of the ribosomes with 1.0 m-KCl to remove the loosely associated factors rendered the ribonucleoprotein particles resistant to cytosol effects. The ribosome-cytosol interactions did not appear to be related to an exchange process, since the released radioactivity was largely degraded to acid-soluble material. In addition, the incubation of native ribosomes with brain cytosol resulted in an almost complete loss in the ability of the ribosomes to participate in cell-free protein synthesis.

Alkylation↗
PubMed1977

Mitochondrial and cytoplasmic ribosomes from mammalian tissues. Further characterization of ribosomal subunits and validity of buoyant-density methods for determination of the chemical composition and partial specific volume of ribonucleoprotein particles.

1. At 0-4 degrees C mitochondrial ribosomes (55S) dissociate into 39S and 29S subunits after exposure to 300mm-K(+) in the presence of 3.0mm-Mg(2+). When these subunits are placed in a medium containing a lower concentration of K(+) ions (25mm), approx. 75% of the subparticles recombine giving 55S monomers. 2. After negative staining the large subunits (20.3nm width) usually show a roundish profile, whereas the small subunits (12nm width) show an elongated, often bipartite, profile. The dimensions of the 55S ribosomes are 25.5nmx20.0nmx21.0nm, indicating a volume ratio of mitochondrial to cytosol ribosomes of 1:1.5. 3. The 39S and 29S subunits obtained in high-salt media at 0-4 degrees C have a buoyant density of 1.45g/cm(3); from the rRNA content calculated from buoyant density and from the rRNA molecular weights it is confirmed that the two subparticles have weights of 2.0x10(6) daltons and 1.20x10(6) daltons; the weights of the two subunits of cytosol ribosomes are 2.67x10(6) and 1.30x10(6) daltons. 4. The validity of the isodensity-equilibrium-centrifugation methods used to calculate the chemical composition of ribosomes was reinvestigated; it is confirmed that (a) reaction of ribosomal subunits with 6.0% (v/v) formaldehyde at 0 degrees C is sufficient to fix the particles, so that they remain essentially stable after exposure to dodecyl sulphate or centrifugation in CsCl, and (b) the partial specific volume of ribosomal subunits is a simple additive function of the partial specific volumes of RNA and protein. The RNA content is linearly related to buoyant density by the equation RNA (% by wt.)=349.5-(471.2x1/rho(CsCl)), where 1/rho(CsCl)=[unk](RNP) (partial specific volume of ribonucleoprotein). 5. The nucleotide compositions of the two subunit rRNA species of mitochondrial ribosomes from rodents (42% and 43% G+C) are distinctly different from those of cytoplasmic ribosomes.

Animals↗
PubMed2002

Structural change of ribosomes during apoptosis: degradation and externalization of ribosomal proteins in doxorubicin-treated Jurkat cells.

Changes in the amount and localization of human ribosomal proteins during apoptosis were determined. When total lysates of Jurkat cells undergoing apoptosis induced by doxorubicin were analyzed by Western blotting, degradation of three ribosomal proteins, S18, L5, and L14, was detected at 48 h after the induction of apoptosis. Decreases in the amounts of these three ribosomal proteins were also observed in ribosome-enriched fractions. These changes were partly abolished by the addition of the pan-caspase inhibitor z-VAD-fmk. Moreover, formation of the 80S ribosome complex appeared to be inhibited at 48 h after apoptosis induction. On the other hand, the rate of protein synthesis, assessed by measuring the incorporation of [35S]Met into bulk proteins, decreased as early as 12 h after the addition of doxorubicin. These results indicate that changes in the amount of ribosomal proteins and the overall structure of ribosomes in apoptosing cells occur after protein synthesis declines. Finally, analyses by flow cytometry, immunofluorescence, and Western blotting showed that six ribosomal proteins, S15, P0, L5, L6, L36a, and L41, were relocalized and expressed at the cell surface during apoptosis. The above results collectively indicate that ribosomes are structurally altered in apoptotic cells following inactivation of protein synthesis.

Antineoplastic Agents↗
PubMed2004

Crosslinking of ribosomal proteins to RNA in maize ribosomes by UV-B and its effects on translation.

Ultraviolet-B (UV-B) photons can cause substantial cellular damage in biomolecules, as is well established for DNA. Because RNA has the same absorption spectrum for UV as DNA, we have investigated damage to this cellular constituent. In maize (Zea mays) leaves, UV-B radiation damages ribosomes by crosslinking cytosolic ribosomal proteins S14, L23a, and L32, and chloroplast ribosomal protein L29 to RNA. Ribosomal damage accumulated during a day of UV-B exposure correlated with a progressive decrease in new protein production; however, de novo synthesis of some ribosomal proteins is increased after 6 h of UV-B exposure. After 16 h without UV-B, damaged ribosomes were eliminated and translation was restored to normal levels. Ribosomal protein S6 and an S6 kinase are phosphorylated during UV-B exposure; these modifications are associated with selective translation of some ribosomal proteins after ribosome damage in mammalian fibroblast cells and may be an adaptation in maize. Neither photosynthesis nor pigment levels were affected significantly by UV-B, demonstrating that the treatment applied is not lethal and that maize leaf physiology readily recovers.

Dose-Response Relationship, Radiation↗
PubMed1987

Starvation-induced alterations of ribosomal protein phosphorylation in Bombyx mori L. Evidence for different phosphorylation kinetics in free and membrane-bound ribosomes.

In the posterior silk gland of Bombyx mori, ribosomal protein S1, homologous to S6 in mammals, is partially phosphorylated in a normally fed animal. Before the first meal of the fifth larval instar, S1 is completely dephosphorylated. Likewise, starvation induces rapid dephosphorylation of the protein in both free and membrane-bound ribosomes. Upon refeeding after 48 h of starvation, S1 becomes phosphorylated again, first on membrane-bound ribosomes, then on free ribosomes, with a lag time of about 3 h. Following 48 h of refeeding, the most highly phosphorylated form of S1 predominates in both populations of ribosomes. These variations in phosphorylation are correlated with the level of protein synthesis in the posterior silk gland, 70% of the ribosomes occurring in polysomes upon feeding and only 30% upon starvation [Prudhomme, J.-C. & Couble, P. (1979) Biochimie (Paris) 61, 215-227]. After in vivo 32P labelling, the phosphopeptides of S1 from free and membrane-bound ribosomes were found to be identical and phosphoserine (only) was found in each S1. These results suggest the involvement of S1 phosphorylation in the regulation of protein synthesis at the translational level and the existence of at least two different pathways controlling this phosphorylation: one for the free ribosomes, the other for the membrane-bound ribosomes.

Animals↗
PubMed1997

Different consequences of incorporating chloroplast ribosomal proteins L12 and S18 into the bacterial ribosomes of Escherichia coli.

We have incorporated chloroplast ribosomal proteins (R-proteins) L12 and S18 into Escherichia coli ribosomes and examined the hybrid ribosomes for their ability to form polysomes in vivo and perform poly(U)-dependent poly(Phe) synthesis in vitro. The rye chloroplast S18 used for the experiment is a highly divergent protein (170 amino acid residues; E. coil S18, 74 residues), containing a repeating, chloroplast-specific, heptapeptide motif, and has amino acid sequence identity of only 35% to E. coli S18. When expressed in E. coli, chloroplast S18 was assembled in E. coli ribosomes. The latter formed polysomes in vivo at about the same rate as the host ribosomes, indicating that the replacement of E. coli S18 with its chloroplast homologue has only a minor, if any, effect on function. The L12 protein is much more conserved in sequence and chain length, and is known to have a very important function. The Arabidopsis chloroplast L12 used in the experiment was incorporated into E. coli 50S subunits that associated with the 30S subunits to form ribosomes, but the latter were unable to form polysomes. This result indicates functional inactivation of E. coil ribosomes by a chloroplast R-protein. To further confirm this result, we overproduced chloroplast L12 through the use of a secretion vector and purified the protein to homogeneity. Chloroplast L12 could be efficiently incorporated in vitro into L7/12-lacking E. coli ribosomes, but the hybrid ribosomes were totally inactive in poly(U)-dependent poly(Phe) synthesis. Computer modeling of the spatial structure of all known chloroplast L12 proteins (using E. coli L12 coordinates) indicated a 'chloroplast loop' present only in chloroplast L12. The presence of this loop might have a role in the observed inactivation. Taken together with previously reported results (summarized in this paper), it would appear that the features of chloroplast R-proteins concerned with specific functions are more divergent than their assembly properties. We have previously described methods suitable for overproduction and purification of chloroplast R-proteins that are encoded in organellar DNA (approximately 20), but that gave poor yield for those encoded in the nuclear DNA (approximately 45). Here we describe a method that overcomes this problem and allows the purification of nucleus-encoded chloroplast R-proteins in milligram quantities.

Amino Acid Sequence↗
PubMed1971

Precursor ribosomal ribonucleic acid and ribosome accumulation in vivo during the recovery of Salmonella typhimurium from thermal injury.

When cells of S. typhimurium were heated at 48 C for 30 min in phosphate buffer (pH 6.0), they became sensitive to Levine Eosin Methylene Blue Agar containing 2% NaCl (EMB-NaCl). The inoculation of injured cells into fresh growth medium supported the return of their normal tolerance to EMB-NaCl within 6 hr. The fractionation of ribosomal ribonucleic acid (rRNA) from unheated and heat-injured cells by polyacrylamide gel electrophoresis demonstrated that after injury the 16S RNA species was totally degraded and the 23S RNA was partially degraded. Sucrose gradient analysis demonstrated that after injury the 30S ribosomal subunit was totally destroyed and the sedimentation coefficient of the 50S particle was decreased to 47S. During the recovery of cells from thermal injury, four species of rRNA accumulated which were demonstrated to have the following sedimentation coefficients: 16, 17, 23, and 24S. Under identical recovery conditions, 22, 26, and 28S precursors of the 30S ribosomal subunit and 31 and 48S precursors of the 50S ribosomal subunit accumulated along with both the 30 and 50S mature particles. The addition of chloramphenicol to the recovery medium inhibited both the maturation of 17S RNA and the production of mature 30S ribosomal subunits, but permitted the accumulation of a single 22S precursor particle. Chloramphenicol did not affect either the maturation of 24S RNA or the mechanism of formation of 50S ribosomal subunits during recovery. Very little old ribosomal protein was associated with the new rRNA synthesized during recovery. New ribosomal proteins were synthesized during recovery and they were found associated with the new rRNA in ribosomal particles. The rate-limiting step in the recovery of S. typhimurium from thermal injury was in the maturation of the newly synthesized rRNA.

Bacterial Proteins↗
PubMed2001

Hybrid protein between ribosomal protein S16 and RimM of Escherichia coli retains the ribosome maturation function of both proteins.

The RimM protein in Escherichia coli is associated with free 30S ribosomal subunits but not with 70S ribosomes and is important for efficient maturation of the 30S subunits. A mutant lacking RimM shows a sevenfold-reduced growth rate and a reduced translational efficiency. Here we show that a double alanine-for-tyrosine substitution in RimM prevents it from associating with the 30S subunits and reduces the growth rate of E. coli approximately threefold. Several faster-growing derivatives of the rimM amino acid substitution mutant were found that contain suppressor mutations which increased the amount of the RimM protein by two different mechanisms. Most of the suppressor mutations destabilized a secondary structure in the rimM mRNA, which previously was shown to decrease the synthesis of RimM by preventing the access of the ribosomes to the translation initiation region on the rimM mRNA. Three other independently isolated suppressor mutations created a fusion between rpsP, encoding the ribosomal protein S16, and rimM on the chromosome as a result of mutations in the rpsP stop codon preceding rimM. A severalfold-higher amount of the produced hybrid S16-RimM protein in the suppressor strains than of the native-sized RimM in the original substitution mutant seems to explain the suppression. The S16-RimM protein but not any native-size ribosomal protein S16 was found both in free 30S ribosomal subunits and in translationally active 70S ribosomes of the suppressor strains. This suggests that the hybrid protein can substitute for S16, which is an essential protein probably because of its role in ribosome assembly. Thus, the S16-RimM hybrid protein seems capable of carrying out the important functions that native S16 and RimM have in ribosome biogenesis.

Amino Acid Substitution↗
PubMedDate not supplied

[Analysis of ribosomal proteins and ribosomal subunits of pea seeds by electrophoresis in polyacrylamide gel].

The amino acid composition of overall protein of ribosomes and ribosomal subunits of pea seeds has been found typical of ribosomal protein. Electrophoresis in polyacrylamide gel demonstrates that proteins extracted by the solution of 3 M LiCl-4 M urea from purified ribosomes of pea seeds move towards the cathode at pH 2.2 and separate into 41 components. Electrophoresis in a tris-glycine buffer at pH 9.2 does not reveal any substance corresponding to acid proteins. Similar distribution patterns are observed when ribosomal particles are isolated with or without triton (0,5%). The treatment of ribosomes by deoxycholate results in some changes, depending on the detergent concentration. All the protein components detected in ribosomes, except one, are present in the subunits. Proteins of large and small ribosome subunits produced 26 and 21 components respectively in polyacrylamide gel electrophoresis. The distribution patterns of proteins of the two subunits appear to be different. The majority of the components of the large and small subunits differ in mobility. The data obtained suggest considerable specificity of the protein composition of 60S and 40S subunits of 80S ribosomes in higher plants.

Electrophoresis, Polyacrylamide Gel↗
PubMed1975

Preferential inhibition by homopolyribonucleotides of the methylation of ribosomal ribonucleic acid and disruption of the production of ribosomes in a rat tumor.

The literature indicates that some mechanism other than the interferon or host-mediated immune enhancement might also be responsible for an antitumor effect of polyinosinate-polycytidylate [poly(I)-poly(C)]. We have examined the effect of this drug on the synthesis of ribosomes and other macromolecules in a rat tumor, the Novikoff ascites hepatoma. The nucleolus was one of the primary targets affected by the administration of poly(I)-poly(C) in vivo. A progressive decline of the activity of nucleolar ribosomal RNA methylases began within 2 hr, followed by a decline of the nucleolar RNA content. The activity of nucleolar RNA polymerase was inhibited only at later time intervals. Labeling of tumor macromolecules in vivo revealed that the methylation of ribosomal RNA and the production of ribosomes, particularly in the small subunits, were immediately and progressively affected, followed by inhibition of the synthesis of DNA, RNA, and protein at later times. In addition, poly(I)-poly(C) also induced disaggregation of polyribosomes and restricted the movements of nuclear RNA to cytoplasm and of cytoplasmic protein to nucleus. These in vivo effects of poly(I)-poly(C) on tumor cells was observed neither on the host livers nor on livers of normal rats. Studies on isolated nucleoli showed that the in vitro addition of polyinosinate and several other compounds actively inhibited tumor ribosomal RNA methylases but were devoid of inhibitory effect against liver ribosomal RNA methylases; these results augment other studies in the literature in suggesting a selective effect of the polyinosinate moiety on tumor cells. We conclude from this study that initial impairment of the methylation of ribosomal precursor RNA, following exposure of tumor cells to poly(I)-poly(C), is responsible for the destruction of ribosomes, preferentially the small subunits, during the maturation processes. Failure to provide new ribosomes thus triggers the events limiting the growth of tumor cells.

Animals↗
PubMed2002

Enzymatic specificity of three ribosome-inactivating proteins against fungal ribosomes, and correlation with antifungal activity.

Ribosome-inactivating proteins (RIPs) are enzymes that cleave a specific adenine base from the highly conserved sarcin/ricin (S/R) loop of the large ribosomal RNA, thus arresting protein synthesis at the translocation step. In the present study, we employed three RIPs to dissect the antifungal activity of RIPs as plant defense proteins. We measured the catalytic activity of RAT (the catalytic A-chain of ricin from Ricinus communis L.), saporin-S6 (from Saponaria officinalis L.), and ME (RIP from Mirabilis expansa R&P) against intact ribosomal substrates isolated from various pathogenic fungi. We further determined the enzymatic specificity of these three RIPs against fungal ribosomes, from Rhizoctonia solani Kuhn, Alternaria solani Sorauer, Trichoderma reesei Simmons and Candida albicans Berkhout, and correlated the data with antifungal activity. RAT showed the strongest toxicity against all tested fungal ribosomes, except for the ribosomes isolated from C. albicans, which were most susceptible to saporin. RAT and saporin showed higher enzymatic activity than ME against ribosomes from all of the fungal species assayed, but did not show detectable antifungal activity. In contrast, ME showed substantial inhibitory activity against fungal growth. Using N-hydroxysuccinimide-fluorescein labeling of RIPs and fluorescence microscopy, we determined that ME was targeted to the surface of fungal cells and transferred into the cells. Thus, ME caused ribosome depurination and subsequent fungal mortality. In contrast, saporin did not interact with fungal cells, correlating with its lack of antifungal activity.

Catalysis↗
PubMed2001

Changes in ribosome function induced by protein kinase associated with ribosomes of Streptomyces collinus producing kirromycin.

Protein kinase associated with ribosomes of streptomycetes phosphorylates 11 ribosomal proteins. Phosphorylation activity of protein kinase reaches its maximum at the end of exponential phase of growth. When (32)P-labeled cells from the end of exponential phase of growth were transferred to a fresh medium, after 2 h of cultivation ribosomal proteins lost more than 90% of (32)P and rate of polypeptide synthesis increases twice. Protein kinase cross-reacting with antibody raised against protein kinase C was partially purified from 1 M NH(4)Cl wash of ribosomes and used to phosphorylation of ribosomes. Phosphorylation of 50S subunits (L2, L3, L7, L16, L21, L23, and L27) had no effect on the integrity of subunits but affects association with 30 to 70S monosomes. In vitro system derived from ribosomal subunits was used to examine the activity of phosphorylated 50S at poly(U) translation. Replacement unphosphorylated 50S with 50S possessed of phosphorylated r-proteins leads to the reduction of polypeptide synthesis of about 52%. The binding of N-Ac[(14)C]Phe-tRNA to A-site of phosphorylated ribosomes is not affected but the rate of peptidyl transferase is more than twice lower than that in unphosphorylated ribosomes. These results provide evidence that phosphorylation of ribosomal proteins is involved in mechanisms regulating the translational system of Streptomyces collinus.

Anti-Bacterial Agents↗
PubMed1977

Control of ribosomal RNA synthesis in Escherichia coli. II. Ribosomal RNA synthesis in isolated nucleoids.

The effect of amino acid-starvation on the transcription in vitro of overall RNA and ribosomal RNA was investigated using nucleoids prepared from the exponentially growing and the amino acid-starved cells of rel+ and rel- strains of Escherichia coli. In this system, the synthesis of RNA is exclusively due to elongation of the chains which have been initiated in vivo. The amounts of overall and ribosomal RNA synthesized per unit of DNA in the nucleoids were analyzed for each preparation. The following observations have been made. (1) The total RNA synthesis per unit of DNA in the nucleoids from the amino acid-starved rel+ and rel- cells was not significantly different from each other. (2) The preferential ribosomal RNA synthesis occurred in the nucleoids from the growing cells; the ribosomal RNA synthesis was restricted in the nucleoids from the starved rel+ cells, while no restriction was observed in the nucleoids from the starved rel- cells. The results suggest that the ribosomal RNA synthesis is regulated at the initiation or less likely elongation level of the transcription. (3) A ribosomal RNA of a discrete size of about 30S was synthesized in the nucleoids. No mature ribosomal RNA species was produced in this system. The 30S RNA is probably a primary transcript of ribosomal RNA genes containing 23S, 16S and 5S mature ribosomal RNA sequences.

Cell-Free System↗
PubMed1984

The effect of trichloroethylene and acrylonitrile on RNA and ribosome synthesis and ribosome content in Saccharomyces cells.

The effects of trichloroethylene (TCE) and acrylonitrile (ACN) on growth, RNA synthesis, ribosome synthesis, and ribosome content were tested in yeast cells. TCE causes a delay of the growth of a cell culture (prolongation of the lag phase), but does not cause inhibition. Cells exposed to increasing concentrations of ACN show increasing damage, so that, at a certain point of the growth curve, cell division stops altogether. Similar results were obtained when RNA synthesis was investigated: After treatment with TCE, the maximum RNA synthesis of the cell culture was retarded, but subsequently reached the same level as the untreated control cells. In the presence of ACN, however, the rate of RNA synthesis was lowered with increasing ACN concentrations. The same effect was observed upon investigation of ribosome synthesis: Whereas TCE produces only a slight effect, treatment with increasing concentrations of ACN leads to a substantial decrease in ribosome synthesis, and finally to total inhibition. Parallel to this, the content of free and membrane-bound ribosomes is diminished. Obviously, the decrease in ribosome content is caused not only by an inhibition of ribosome synthesis, but also by a degradation of existing ribosomes, as well as by induction of a ribosome-associated RNase.

Acrylonitrile↗