Polysome Levels Research Articles

YbeY, a Heat Shock Protein Involved in Translation in Escherichia coli

Here we provide evidence that YbeY, a conserved heat shock protein with unknown function, is involved in the translation process. ybeY deletion mutants are temperature sensitive and have a significantly reduced thermotolerance. Nonetheless, there appears to be no damage of the protein quality control of mature polypeptides, as the levels of chaperones and proteases are normal and there is no accumulation of aggregates. Rather, the mutation results in a significant reduction in the level of polysomes, and upon a shift to a restrictive temperature (42 degrees C), there is an immediate and severe slowdown of translation. Taken together, the data indicate that YbeY is an important factor for bacterial translation even at 37 degrees C but becomes essential at high temperatures.

Inorganic polyphosphate interacts with ribosomes and promotes translation fidelity in vitro and in vivo

Inorganic polyphosphate is a biological macromolecule consisting of multiple phosphates linked by high-energy bonds. Polyphosphate occurs in cells from all domains of life, and is known to play roles in a diverse collection of cellular functions. Here we examine the relationship between polyphosphate and protein synthesis in Escherichia coli. We report that polyphosphate associates with E. coli ribosomes in vitro. Characterization of this interaction reveals that both long-chain and short-chain polyphosphates interact with the ribosome. Intact 70S ribosomes, as well as 50S and 30S subunits, display a specific interaction with polyphosphate that is mediated primarily by contacts with ribosomal proteins. Additionally, we examined functional consequences of a ppk mutation, which severely reduces levels of intracellular polyphosphate. Extracts from ppk mutants contain lower levels of polysomes than wild-type cells, suggesting a defect in mRNA utilization or the mRNA-ribosome interaction. Ribosomes from wild-type and ppk mutant cells were isolated, and their activities were compared using a polyU RNA in vitro translation assay. While rates of polyphenylalanine synthesis are similar, use of ribosomes from ppk cells results in a misincorporation rate about five times higher compared with the rate observed when ribosomes from wild-type cells are used. Mistranslation rates in vivo were measured directly, and ppk mutants displayed higher readthrough frequencies for two different stop codons. Taken together, these results indicate that polyphosphate plays an important role in maintaining optimal translation efficiency in vivo and in vitro.

Reduced polysome levels and preferential recruitment of a defense gene transcript into polysomes in soybean cells treated with the syringolide elicitor

The bacterial syringolide elicitor induces a hypersensitive defense response (HR) in leaf tissue and cell suspensions of soybean cultivars carrying resistance gene Rpg4. To investigate the possible involvement of translational control of gene expression in the syringolide-induced HR, ribosome profiles and polysome-loading of two gene transcripts were investigated. Sucrose density gradient fractionation of soybean cell extracts was used to demonstrate a syringolide-induced, Rpg4-specific reduction in large polysomes and a concomitant increase in 80S ribosomes, presumably reflecting an overall inhibition of translation initiation. Syringolide treatment also led to an accumulation of chalcone synthase defense gene mRNA, which remained efficiently loaded into large polysomes in spite of a 22% reduction in cellular large polysome levels. In contrast, while mRNA levels of the housekeeping gene actin remained unchanged following syringolide treatment, the amount of actin mRNA loaded into large polysomes was decreased by 49%. Thus, the translational machinery appeared to selectively exclude a subpopulation of actin transcripts while simultaneously maintaining efficient loading of transcripts for the defense gene chalcone synthase. These data suggest that elicited soybean cells utilize translational control of gene expression during the shift from normal metabolism to defense response activation.

Differential mRNA translation contributes to gene regulation under non-stress and dehydration stress conditions in Arabidopsis thaliana.

Translational regulation was evaluated for over 2000 genes by measurement of the proportion of individual mRNA species in polysomal (PS) complexes in leaves of non-stressed and moderately dehydration-stressed Arabidopsis. The amount of each mRNA in polysomes ranged from 23 to 97% in non-stressed leaves and was significantly reduced for a large portion of the genes (71%) in response to dehydration. The effect of dehydration on translational status varied extensively between mRNA species. Sixty per cent of the dehydration-inducible mRNAs with twofold or greater increase in abundance maintained PS levels in response to water-deficit stress, while 40% showed impaired ribosome loading (RL). PS association declined significantly for 92% of the mRNAs that displayed a strong decrease in abundance, indicating a relationship between translation and decreased gene transcription and/or mRNA stability. Interestingly, many mRNAs that encode proteins of similar biological function displayed coordinate translational regulation. Thus, the abundance of PS mRNA may provide a more accurate estimate of gene expression than total cellular mRNA because of extensive differential translational regulation.

Biomonitoring of Gulf of Patras, N. Peloponnesus, Greece. Application of a biomarker suite including evaluation of translation efficiency in Mytilus galloprovincialis cells

Specimens of Mytilus galloprovincialis were placed in bow nets and immersed at 3–10 m depth in a clean coastal region (reference area), Itea, and two marine stations along Gulf of Patras, N. Peloponnesus, Greece. One site is near the estuaries of the Glafkos River, which are influenced by local industrial and urban sources (Station 1); the second site, Agios Vasilios, has no evident organic pollution but is enriched in metals, particularly zinc (Station 2). One month after immersion, digestive glands were removed from the mussels and tested for lysosomal membrane stability, metallothionein content, and translational efficiency of ribosomes. In addition, gill cells were isolated and their micronuclei content was determined. Compared with the reference samples, mussels transplanted to Gulf of Patras showed a significant increased lysosomal membrane permeability and metallothionein content, reduced polysome levels, and increased chromosomal damage in relation to the contamination burden of each sampling area. Also, runoff ribosomes from mussels transplanted to Gulf of Patras (that is, ribosomes stripped of endogenous messengers and peptidyl- or/and aminoacyl-tRNAs) were less efficient at initiating protein synthesis in an in vitro–translation system than those prepared from reference samples. The whole set of data suggests that the degree of Gulf of Patras pollution differs between different sites and depends on the proximity of urban sewage and industrial outfalls. In addition, our results emphasize the importance of protein synthesis regulation as a component of the cellular stress response.

Water‐deficit‐induced translational control in Nicotiana tabacum

ABSTRACTThe effect of prolonged water deficit on mRNA translation was quantitatively analysed in apical and basal leaves of whole tobacco (Nicotiana tabacum) plants. The level of large polysomes (six or more ribosomes per mRNA) was significantly higher in apical than basal leaves under well‐watered conditions. In both young and old leaves, water deficit caused a progressive reduction in levels of polysomes with concomitant increases in 80S monosomes, indicative of reduced initiation of translation. Despite the global reduction in polysome formation over 144 h of water deficit, the water‐deficit‐induced putative lipid transfer protein (ltp) mRNA was associated with large polysomes and LTP content increased. Osmotin (osm) mRNA, another water‐deficit‐induced transcript, also remained associated with large polysomes during prolonged water deficit. In contrast, mRNAs encoding the non‐stress proteins ribulose bisphosphate carboxylase/oxygenase small subunit (rbcS) and eukaryotic initiation factor 4A (eIF4A) decreased in abundance and shifted to small polysomes and non‐polysomal complexes, indicating that initiation of translation of these mRNAs was impaired by water deficit. These results show that translational regulation is a component of the water‐deficit response and the differential translation of individual mRNAs is distinct in leaves of different age.

Evaluation of Calcium Channel Blockers as Potential Hepatoprotective Agents in Oxidative Stress Injury of Perfused Hepatocytes

The aim of this study was to investigate the effects of calcium channel blockers on tertbutyl hydroperoxide (TBH) induced liver injury using isolated perfused rat hepatocytes. Rat hepatocytes were immobilized in agarose threads and perfused with Williams E medium. Hepatocyte injury was induced by the addition of tertbutyl hydroperoxide (1 mM) to the perfusion medium 30 min after the addition of either verapamil or diltiazim. Hepatocyte injury was observed by monitoring the functional and metabolic competence of hepatocytes or by ultrastructural morphological examination of hepatocytes. Verapamil (0.5 mM) reduced lactate dehydrogenase leakage in TBH-injured hepatocytes as compared to the controls (154+/-11% vs. 247+/-30%). Lipid peroxides production was reduced after verapamil pretreatment as compared to the controls and oxygen consumption was increased by pretreatment of hepatocytes with verapamil. Verapamil pretreatment increased the protein synthesis activity at both levels of granular endoplasmic reticulum and free polysomes in cytoplasm and decreased ATPase activity. Diltiazem was qualitatively effective as verapamil. It is concluded that in hepatocyte oxidative injury, calcium channel blockers exhibited hepatoprotective properties. The hepatoprotective effect of calcium channel blockers was accompanied by a decrease in ATPase activity, which may implicate a normalization of Ca2+i after TBH intoxication.

HnRNP A2 and hnRNP L Bind the 3′UTR of Glucose Transporter 1 mRNA and Exist as a Complex in Vivo

Recent work identified an RNA binding protein whose presence in brain tumors correlated with translational repression of Glut1 expression. RNase T1 mapping demonstrated that this protein bound an AU-rich response element (AURE) in the Glut1 3′UTR. Facilitated by its differential expression in brain tumor cytosols, we identified this Glut1 RNA binding protein as hnRNP A2. Studies further demonstrated that hnRNP A2 was the major Glut1 RNA binding activity in other cell lines. Recombinant hnRNP A2 exhibited equivalent Glut1 RNA binding specificity, quite distinct from the related AURE binding protein hnRNP A1. These data indicate that hnRNP A2 is the Glut1 AURE binding protein whose cytoplasmic expression in gliomas is associated with translational repression and mRNA instability. Using this approach, we also identified the other major Glut1 3′UTR RNA binding activity as hnRNP L. Stimuli (hypoxia and hypoglycemia) which increase Glut1 mRNA stability selectively decreased polysomal levels of hnRNP A2 and L. Immunoprecipitation demonstrated that hnRNP A2 and L exist as a complex in vivo. As a result of these and other studies, we conclude that hnRNP A2 and L associate in vivo and independently bind the 3′UTR of Glut1 mRNA.

Nip7p interacts with Nop8p, an essential nucleolar protein required for 60S ribosome biogenesis, and the exosome subunit Rrp43p.

NIP7 encodes a conserved Saccharomyces cerevisiae nucleolar protein that is required for 60S subunit biogenesis (N. I. T. Zanchin, P. Roberts, A. DeSilva, F. Sherman, and D. S. Goldfarb, Mol. Cell. Biol. 17:5001-5015, 1997). Rrp43p and a second essential protein, Nop8p, were identified in a two-hybrid screen as Nip7p-interacting proteins. Biochemical evidence for an interaction was provided by the copurification on immunoglobulin G-Sepharose of Nip7p with protein A-tagged Rrp43p and Nop8p. Cells depleted of Nop8p contained reduced levels of free 60S ribosomes and polysomes and accumulated half-mer polysomes. Nop8p-depleted cells also accumulated 35S pre-rRNA and an aberrant 23S pre-rRNA. Nop8p-depleted cells failed to accumulate either 25S or 27S rRNA, although they did synthesize significant levels of 18S rRNA. These results indicate that 27S or 25S rRNA is degraded in Nop8p-depleted cells after the section containing 18S rRNA is removed. Nip7p-depleted cells exhibited the same defects as Nop8p-depleted cells, except that they accumulated 27S precursors. Rrp43p is a component of the exosome, a complex of 3'-to-5' exonucleases whose subunits have been implicated in 5.8S rRNA processing and mRNA turnover. Whereas both green fluorescent protein (GFP)-Nop8p and GFP-Nip7p localized to nucleoli, GFP-Rrp43p localized throughout the nucleus and to a lesser extent in the cytoplasm. Distinct pools of Rrp43p may interact both with the exosome and with Nip7p, possibly both in the nucleus and in the cytoplasm, to catalyze analogous reactions in the multistep process of 60S ribosome biogenesis and mRNA turnover.

Synthetic lethal interactions with conditional poly(A) polymerase alleles identify LCP5, a gene involved in 18S rRNA maturation.

To identify new genes involved in 3'-end formation of mRNAs in Saccharomyces cerevisiae, we carried out a screen for synthetic lethal mutants with the conditional poly(A) polymerase allele, pap1-7. Five independent temperature-sensitive mutations called Icp1 to Icp5 (for lethal with conditional pap1 allele) were isolated. Here, we describe the characterization of the essential gene LCP5 which codes for a protein with a calculated molecular mass of 40.8 kD. Unexpectedly, we found that mutations in LCP5 caused defects in pre-ribosomal RNA (pre-rRNA) processing, whereas mRNA 3'-end formation in vitro was comparable to wild-type. Early cleavage steps (denoted A0 to A2) that lead to the production of mature 18S rRNA were impaired. In vivo depletion of Lcp5p also inhibited pre-rRNA processing. As a consequence, mutant and depleted cells showed decreased levels of polysomes compared to wild-type cells. Indirect immunofluorescence indicated a predominant localization of Lcp5p in the nucleolus. In addition, antibodies directed against Lcp5p specifically immunoprecipitated the yeast U3 snoRNA snR17, suggesting that the protein is directly involved in pre-rRNA processing.

Nop2p is required for pre-rRNA processing and 60S ribosome subunit synthesis in yeast.

To investigate the function of the nucleolar protein Nop2p in Saccharomyces cerevisiae, we constructed a strain in which NOP2 is under the control of a repressible promoter. Repression of NOP2 expression lengthens the doubling time of this strain about fivefold and reduces steady-state levels of 60S ribosomal subunits, 80S ribosomes, and polysomes. Levels of 40S subunits increase as the free pool of 60S subunits is reduced. Nop2p depletion impairs processing of the 35S pre-rRNA and inhibits processing of 27S pre-rRNA, which results in lower steady-state levels of 25S rRNA and 5.8S rRNA. Processing of 20S pre-rRNA to 18S rRNA is not significantly affected. Processing at sites A2, A3, B1L, and B1S and the generation of 5' termini of different pre-rRNA intermediates appear to be normal after Nop2p depletion. Sequence comparisons suggest that Nop2p may function as a methyltransferase. 2'-O-ribose methylation of the conserved site UmGm psi UC2922 is known to take place during processing of 27S pre-rRNA. Although Nop2p depletion lengthens the half-life of 27S pre-RNA, methylation of UmGm psi UC2922 in 27S pre-rRNA is low during Nop2p depletion. However, methylation of UmGm psi UC2922 in mature 25S rRNA appears normal. These findings provide evidence for a close interconnection between methylation at this conserved site and the processing step that yields the 25S rRNA.

C-terminal Trimerization, but Not N-terminal Trimerization, of the Reovirus Cell Attachment Protein Is a Posttranslational and Hsp70/ATP-dependent Process

The C-terminal globular head of the lollipop-shaped final sigma1 protein of reovirus is responsible for interaction with the host cell receptor. Like the N-terminal fibrous tail, it has its own trimerization domain. Whereas N-terminal trimerization (formation of a triple alpha-helical coiled coil) occurs at the level of polysomes (i.e. cotranslationally) and is ATP-independent, C-terminal trimerization is a posttranslational event that requires ATP. Coprecipitation experiments using anti-Hsp70 antibodies and truncated final sigma1 proteins synthesized in vitro revealed that only regions downstream of the N-terminal alpha-helical coiled coil were associated with Hsp70. Hsp70 was also found to be associated with nascent final sigma1 chains on polysomes as well as with immature postribosomal final sigma1 trimers (hydra-like intermediates with assembled N termini and unassembled C termini). These latter structures were true intermediates in the final sigma1 biogenetic pathway since they could be chased into mature final sigma1 trimers with the release of Hsp70. Thus, unlike N-terminal trimerization, C-terminal trimerization is Hsp70- and ATP-dependent. The involvement of two mechanistically distinct oligomerization events for the same molecule, one cotranslational and one posttranslational, may represent a common approach to the generation of oligomeric proteins in the cytosol.

Rubisco, rubisco activase and ribulose-5-phosphate kinase gene expression and polypeptide accumulation in a tobacco mutant defective in chloroplast protein synthesis

Expression of the genes for ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; rbcS and rbcL), Rubisco activase (rca) and ribulose-5-phosphate (Ru5-P) kinase (prk) and accumulation of the polypeptides was examined in chlorophyllous and chlorotic sectors of the DP1 mutant of Nicotiana tabacum. Plastids from chlorotic sectors of this variegated plastome mutant contained 30S and 50S ribosomal subunits, but had abnormally low levels of plastid polysomes. Consequently, mutant plastids were translationally repressed, unable to synthesize plastid-encoded polypeptides including the large subunit of Rubisco despite the presence of the corresponding mRNAs. Transcripts of rbcS accumulated to near wild type levels in chlorotic sectors, but there was little accumulation of the Rubisco small subunit (SS) polypeptide or holoenzyme. Messenger-RNA isolated from chlorotic sectors effectively directed the synthesis of Rubisco SS in vitro suggesting that posttranslational factors were responsible for the decrease in Rubisco SS abundance. Transcripts of rca and prk also accumulated to near wild type levels in chlorotic sectors and a diurnal rhythm in the abundance of rca mRNA was detected in green and chlorotic sectors. Despite the low abundance of Rubisco holoenzyme in chlorotic sectors, Rubisco activase and Ru5-P kinase polypeptides accumulated to significant levels. Activities of Rubisco and Ru5-P kinase paralleled protein levels, indicating that active forms of these enzymes were present in chlorotic sectors. The data indicate that the developmental events governing the accumulation of Rubisco activase and Ru5-P kinase polypeptides and the diurnal regulation of rca expression were not dependent on the attainment of photosynthetically competent plastids or the accumulation of Rubisco.

Protein Synthesis and Breakdown during Heat Shock of Cultured Pear (Pyrus communis L.) Cells.

Cultured pear (Pyrus communis L. cv Passe Crassane) cells were subjected to temperatures of 39, 42, and 45[deg]C. Heat-shock protein (hsp) synthesis was greater at 30[deg]C than at temperatures above 40[deg]C and continued for up to 8 h. Both cellular uptake of radiolabeled methionine and total protein synthesis were progressively lower as the temperature was increased. Polysome levels decreased immediately when cells were placed at 39 or 42[deg]C, although at 39[deg]C the levels began to recover after 1 h. In cells from both temperatures, reassembly occurred after transfer of cells to 25[deg]C Four heat-shock-related mRNAs[mdash]hsp17, hsp70, and those of two ubiquitin genes[mdash]all showed greatest abundance at 39[deg]C and decreased at higher temperatures. Protein degradation increased with time at 42 and 45[deg]C, but at 39[deg]C it increased for the first 2 h and then decreased. In the presence of cycloheximide, which prevented hsp synthesis, protein degradation at 39[deg]C was as great as that at 45[deg]C in the absence of cycloheximide. The data suggest that hsps may have a role in protecting proteins from degradation at the permissive temperature of 39[deg]C. At temperatures high enough to inhibit hsp synthesis, protein degradation was enhanced. Although ubiquitin may play a role in specific protein degradation, it does not appear to be involved in increased protein degradation occurring above 40[deg]C.

A cold-sensitive mutation in 16S rRNA provides evidence for helical switching in ribosome assembly.

A C-->U substitution at position 23 of 16S rRNA confers a dominant, cold-sensitive phenotype. The mutation changes the G11-C23 base pair of the 5' terminal pseudoknot helix to a G-U pair, which is predicted to cause significant weakening of the helix. Ribosomes containing mutant RNA are impaired in assembly and function at low temperature. Cells expressing the C23U mutation have decreased polysome levels and accumulate free 30S and 50S subunits and particles that resemble those previously observed in cold-sensitive alleles of ribosomal protein S5 and in in vitro reconstitution of 30S subunits carried out at low temperature. Three second-site suppressor mutations suggest that cold sensitivity is caused by competition between the 5' helix and an alternative helix formed by base-pairing of the upstream precursor sequence with one strand of the mature helix. Cold sensitivity appears to be relieved by destabilization of the competing precursor helix relative to the mature helix.

The effect of aging on protein synthesis in the yeast Saccharomyces cerevisiae

The protein synthetic rate in the yeast S. cerevisiae, measured by the incorporation of radioactive amino acids per unit amount of proteins, decreased linearly with age reaching 50% of the rate of 2nd generation cells (young cells) in 20th generation cells (old cells), whereas the RNA content of the old cells was increased three times. Using a cell-free system for poly(U)-directed poly-phenylalanine synthesis, the activity of run-off ribosomes from old cells was shown to be about 40% less than the activity of ribosomes from young cells and the polysome level in old cells was much decreased compared to that in young cells. However, as protein content was increased twice in 20 generations, the cell is considered to maintain a constant level of protein synthesis during the process of aging compensating the decrease in the activity of ribosomes. Thus, it is likely that the decrease in the synthesis of certain proteins whose requirement was raised by the increase in cell volume, which is twice the increase in protein content, causes prolongation of the unbudded phase in old cells.

The formation and translational activity of polysomes from developing lupin seeds

The formation and in vitro translational activity of total, free and membrane‐bound polysomes from various stages of developing cotyledons of yellow lupin seeds (Lupinus luteus L. cv. Iryd) has been investigated. The early stages of seed formation were characterized by a low level of polysomes that progressively increased. The main features of the cotyledons at the middle phase of development were full expansion growth and the highest amount of polysomes observed in all three poly so me fractions. In The final stages of emhryogenesis. the seed dehydration was accompanied by‐gradual loss of all types of polysomes, at which the membrane‐attached formations were degraded earlier than the free ones. By means of a wheat germ‐derived cell‐free system for protein synthesis, a correlation was demonstrated between cotyledon growth, polysome formation and their capacity for protein synthesis in vitro. As compared to the free polysomes, both the total and membrane‐bound formations were more active in protein synthesis in vitro. Analysis of the translational products by means of immunoprecipitation and gel electrophoresis followed by fluorography showed that only membrane‐bound polysomes produced polypeptides of higher molecular weight, including subunits of a legumin‐like protein.

Cytokinin-promoted Polyribosome Formation in Excised Cucumber Cotyledons

Polyribosome (polysome) levels based on total ribosomal materials in excised etiolated cotyledons of Cucumis sativus L. cv. Ohio were examined during incubation with or without N 6 -benzyladenine (BA) in the dark. Within the first 2 h after excision, polysome levels in both cotyledons with and without BA increased about 5-fold. The polysome level in control cotyledons subsequently declined, approximating the initial level after 12-18h. In BA-treated cotyledons, however, it remained high during the entire period of incubation. BA application to the water-pretreated (18h) cotyledons also increased the polysome level and did not affect RNase activity or RNA content. BA-promoted polysome formation was inhibited by α-amanitin and cordycepin but not by 5-fluorouracil. These results are consistent with the hypothesis that cytokininpromoted polysome formation depends on de novo synthesis of mRNA but not of rRNA.

Ribosomal and polyadenylated RNA content of rubber tree latex, association with sucrose level and latex pH

Poly(A) content of latex polysomes in tapped Hevea trees of different age and clonal origin varied from 0.1 μg to 0.5 μg ml −1 latex cytosol indicating poly(A) +RNA levels of 1.5 μg – 7.5 μg ml −1 and between 3% and 7.5% in proportion to rRNA. The level of rRNA was in the range 43 μg – 120 μg ml −1. The poly(A) +RNA exhibited a polydisperse sedimentation pattern with prominent peaks at 16 S, 20 S and 24 S, and an apparent mean size of 2270 nucleotides. Clonal differences in rRNA were significant and within different clonal trials were associated with variations in the level of latex sucrose and in latex pH suggesting an association with the activity of latex glycolysis. Level of polysomal poly(A), also in proportion to rRNA, was significantly higher in clone PB 217 than in clones GT 1 and PB 235 exhibiting much lower sucrose content of latex. Bark treatment with ethephon increasing latex pH, sucrose utilization and latex yield increased the levels of rRNA and particularly of poly(A) +RNA. This increase did not result in an increase of soluble proteins and may thus be concerned with synthesis of proteins bound to latex structures. Low levels of polysomes for cytoplasmic structure formation may be involved in association of low sucrose with latex vessel senescence.

Modulation of membrane-associated protein synthesis in rat brain cells by the anti-oxidant 2-ethyl-6-methyl-3-oxypyridine.

Intraperitoneal injection of different amounts of 6-methyl-2-ethyl-3-oxypyridine (6M2E3OP) to 3- and 18-month-old rats led to significant reduction of translating activity in vitro of membrane-bound polysomes of rat brain cells, but nor of free polysomes. This was more marked in the case of endoplasmic membranes of 18-month-old animals than in these of 3-month-old ones. Separation of polysomes from membranes by Triton X-100 resulted in restoration of template activity to the level of free polysomes. Forty eight hours after intraperitoneal injection of 6M2E3OP to 3- and 18-month-old rats the substance was found, by HPLC, only in endoplasmatic reticulum membranes of brain cells, but not in their cytoplasm. The xenobiotic did not change the age-dependent ratio of free and membrane-bound brain polysomes. At the same time the substance significantly inhibited the mean rate of synthesis of the longest polypeptide chains (MW 28-42,000 daltons) in cells of old animals.