[Ribonucleic acid as an intermediary and its role as a matrix in protein biosynthesis].
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Protein Biosynthesis↗
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Why do two EF-Tu molecules act in the elongation cycle of protein biosynthesis?
In the elongation cycle of bacterial protein biosynthesis, the binding of aminoacyl-tRNA (aa-tRNA) to the A-site of mRNA-programmed ribosomes is mediated by elongation factor Tu (EF-Tu) and associated with the hydrolysis of GTP. Recently, in the case of cognate aa-tRNA, the participation of two GTP molecules has been implicated in this reaction. These are likely to be involved in preventing the indiscriminate binding of aa-tRNA to the ribosomal A-site. This article integrates this unexpected finding with our current knowledge of the structure-function relationships of the macro-molecules involved in the elongation cycle.
Peptide Chain Elongation, Translational↗
[RNA biosynthesis in mitochondria under conditions of prolonged inhibition of protein biosynthesis in rat liver cytoplasm].
When cytoplasmic protein synthesis is inhibited by cycloheximide (CHI) in vivo synthesis of water-soluble mitochondrial proteins and of mitochondrial RNA is decreased. These changes measured in isolated rat liver mitochondria are similar to those observed in vivo and correlate with the changes the synthesis of water-soluble proteins in mitochondria. When the cytoplasmic fraction (30,000 g-supernatant) had been added to the mitochondria showing decreased RNA synthesis, the RNA synthesis increased to the control level (the incubation conditions were favourable for the protein transport from microsomes to mitochondria). RNA synthesis in mitochondria was not stimulated by cytoplasmic fractions from the CHI-pretreated rats. After prolonged dialysis these fraction stimulated RNA synthesis even to a greater extent than cytoplasmic fractions from the untreated animals. Mitochondrial RNA polymerase activity (measured in mitochondrial extracts supplemented with exogenous DNA) was higher in extracts of mitochondria from livers of normal rats than in extracts of mitochondria from livers of animals injected with CHI.
Animals↗
Amino acid substitutions in protein biosynthesis. Poly(A)-directed polyphenylalanine synthesis.
The fidelity of protein biosynthesis in vitro was studied quantitatively in a well defined system that employed poly(A) as a message for the elaboration of phenylalanine-containing polypeptides from Escherichia coli phenylalanyl-tRNALys. Admixture of phenylalanyl-tRNALys and lysyl-tRNALys in three different ratios resulted in the efficient formation of peptides that contained the amino acids in the same ratios in which they had been utilized in the individual incubation mixtures. The incorporation was also shown to be codon-specific in a quantitative sense; the poly(A)-directed incorporation of [14C]phenylalanine from phenylalanyl-tRNALys was unaffected by [3H]phenylalanyl tRNAPhe, by arginyl-tRNA (one species of which responds to the codon triplet AGA) or by unfractionated E. coli tRNA. These findings suggest that the transfer of amino acids from (misacylated) tRNAs into polypeptides in vitro is as predicted by the adapter hypothesis and that such systems can operate with sufficient fidelity to permit the preparation of proteins having defined amino acid substitutions.
Amino Acyl-tRNA Synthetases↗
[Morphometric and autoradiographic analysis of protein biosynthesis and the transcription apparatus in sympathetic neurons of normal and partially sympathectomized rats].
Cytological analysis of protein biosynthesis has been performed in sympathetic neurons of partially desympathized rats 1 and 6 months of age. Pronounced increase in the area of EPS-membranes, the amount of membrane-bound ribosomes, fragmentation coefficient of EPS cisterns, the amount of poly- and monoribosomes as well as heightened activity of protein biosynthesis might be related to its intensified function in desympathized rats. According to the data of autoradiographic analysis the increase in template activity of neuronal chromatin also occurs especially in the nucleolar area. The intensity of changes correlates with the degree of desympathization.
Age Factors↗
Heterogeneity in the production of collagens and fibronectin by morphologically distinct clones of a human tumor cell line: evidence for intratumoral diversity in matrix protein biosynthesis.
Recent studies of murine tumor models and certain human tumor cell lines have provided evidence for intratumor heterogeneity in expression of extracellular matrix receptors and in the elaboration of matrix-degrading enzymes. However, little is known about possible intratumoral heterogeneity in the production of matrix macromolecules. We have, therefore, examined the biosynthesis and secretion of matrix proteins by cells derived from a polyclonal human cell line (JH-17) established from a large cell undifferentiated carcinoma of the lung. For the present studies, we focused on the production of collagens and structural glycoproteins by two phenotypically different aneuploid clones, designated C13 and C22. These clones were distinctive in their inability to grow in soft agar or to form tumors in nude mice and had identical DNA contents. Tumor cells were labeled with [3H]proline and the newly synthesized proteins accumulating in the culture medium were identified using biochemical and immunologic techniques. Clone C13 secreted at least three genetically distinct collagens, including type V procollagen (PC), type IV procollagen, and a type VIII-like collagen. By contrast, the clone C22 synthesized fibronectin, and a single bacterial collagenase-sensitive and pepsin-resistant component consistent with type I trimer. These studies emphasize the potential diversity of matrix proteins synthesized by neoplastic cells and suggest that there is intratumoral heterogeneity in matrix protein biosynthesis in vivo. These studies further suggest that tumor-derived matrix may be altered during tumor progression or cell selection in vivo.
Carcinoma, Small Cell↗
Aqueous humor-stimulated protein biosynthesis in ocular tissue fibroblast culture.
Dilute concentrations of aqueous humor stimulate DNA synthesis and cell division in monolayer fibroblast culture of rabbit skin and human and rabbit Tenon's capsule. We used [35S]-methionine to study 20% aqueous humor's effect on protein biosynthesis. A non-specific stimulator, 10% fetal bovine serum, was also used for comparison. Incorporation of radioactivity into acid-precipitable material was measured in both the fibroblasts and the media containing extracellular labeled proteins. The extracellular and intracellular labeled proteins were resolved by gel electrophoresis. Both 20% aqueous humor and 10% fetal bovine serum stimulated increased incorporation of [35S]-methionine into intracellular proteins relative to control values (from fibroblasts maintained in 0.5% fetal bovine serum-supplemented medium). However, 20% aqueous humor caused only a slight increase in labeling of proteins exported into the medium, whereas 10% fetal bovine serum stimulated a several-fold increase in extracellular labeled proteins relative to control values. Gel electrophoresis of labeled proteins showed that the quantitative distribution of extracellular proteins varied depending on the growth stimulator present. We conclude that the protein biosynthesis modulation by aqueous humor differs from that by fetal bovine serum. Aqueous humor may selectively stimulate the synthesis of discrete proteins while a general stimulation occurs with fetal bovine serum.
Animals↗
Compartmentation of free amino acids for protein biosynthesis. Influence of diurnal changes in hepatic amino acid concentrations of the composition of the precursor pool charging aminoacyl-transfer ribonucleic acid.
To investigate further the mechanisms by which amino acids are segregated for protein biosynthesis, the distribution of a pulse of [3H]valine was monitored in hepatic amino acid pools at seven intervals in the diurnal cycle of meal-fed rats. Although each condition was characterized by a unique balance between intracellular and extracellular valine, in every case the specific radioactivity of valyl-tRNA at steady state was higher that that of intracellular valine but below the extracellular value. Further, the specific radioactivity of the valyl-tRNA could be accurately predicted if extracellular and intracellular valine were combined in proportions specified by the transmembrane concentration gradient. These observations not only substantiate our earlier conclusions that the amino acids used for protein synthesis do not originate exclusively from either the intracellular or extracellular pools, but also strengthen our theory that the membrane transport system is the physical basis for such compartmentation. On the basis of these data we present a method for measuring the specific radioactivity of the precursor pool for protein biosynthesis in cases where the actual isolation of the aminoacyl-tRNA is not technically feasible, and also suggest a theoretical basis for interpreting the unequal distribution of both total and [3H]valine between intracellular and extracellular fluids.
Amino Acids↗
Target regulation of protein biosynthesis in retinal ganglion cells during regeneration of the goldfish visual system.
Transected ganglion cells of the goldfish retina demonstrate a marked increase in protein biosynthesis as their axons regrow into a primary target tissue, the optic tectum. In order to examine what role the target tissue may play in regulating the pattern of neuronal protein biosynthesis, the tectum is removed at the time of axotomy. By 10 days after surgery, the production of specific polypeptides including the structural proteins, tubulin and actin, are not affected by tectal ablation. However, during a later phase of regeneration when axons would normally begin to re-connect with the tectum, the appearance of a radiolabeled polypeptide of 300 kDaltons is blocked by tectal ablation. These data suggest that ganglion cells are regulated by target tissues late in the regenerative process perhaps by contact between axons and cells of the tectum.
Animals↗
The effects of polyamines on cardiac protein biosynthesis.
Putrescine, spermine, and spermidine were able to stimulate cell-free protein biosynthesis at low Mg++ ion concentrations. The addition of polyamines to the perfusate of an isolated perfused rat heart preparation caused an increased rate of [14C]phenylalanine incorporation into myocardial protein. Spermine increased the uptake of alpha-aminoisobutyric acid into the myocardium.
Aminoisobutyric Acids↗
Biotin-mediated protein biosynthesis.
The effect of administration of biotin to biotin-deficient rats on protein biosynthesis was studied. Biotin treatment resulted in stimulation by more than twofold of amino acid incorporation into protein, both in vivo and in vitro in rat liver, pancreas, intestinal mucosa and skin. Analysis of the products of amino acid incorporation into liver proteins in vivo and in vitro indicated that the synthesis of some proteins was stimulated more than twofold, but others were not stimulated at all. This indicates a specificity in the stimulation of protein synthesis mediated by biotin.
Animals↗
[Isolation and characterization of casein kinases I and II from rabbit liver. Analysis of their effects on protein biosynthesis in the cell].
Two cAMP-independent protein kinases isolated from rabbit liver extracts phosphorylate casein far more effectively than histones. The first protein kinase consists of one polypeptide chain (Mr = 37,000), utilizes exclusively ATP and is not inhibited in the presence of low heparin and RNA concentrations. The second protein kinase consists of three subunits (Mr = 42,000, 40,000 and 25,000 Da), utilizes both ATP and GTP and is inhibited by low heparin and RNA concentrations. The latter enzyme has Mr approximately 140,000 Da and possesses a polyanion-binding activity. These characteristics allow to relate the above enzymes to casein kinases I and II, respectively. Injection of casein kinase I into frog oocytes results in the inhibition of the rate of amino acid incorporations into the soluble and detergent extractable proteins. Casein kinase II has no effect on the amino acid incorporation into the recipient oocytes.
Animals↗
Fine structure and protein biosynthesis of the rat seminal vesicles under experimental conditions.
The morphology and functional activity of rat seminal vesicles from normal animals were compared to those administered 3 weeks the synthetic ergot alkaloid lisuride hydrogenmaleate (LHM) with or without simultaneous prolactin substitution and to those from rats castrated 3 days previously. The secretory cells in seminal vesicle epithelium of LHM-treated animals showed regressive changes, irrespective to simultaneous prolactin treatment. Castration resulted in a sharp drop of serum testosterone and consequently in a significant decrease in protein biosynthesis of tissue slices. LHM treatment depressed serum prolactin levels, but testosterone levels and protein biosynthesis were in the normal ranges. In LHM-treated, prolactin-substituted animals both the prolactin and testosterone levels were low, but amino acid incorporation of tissue slices was unaltered. The results indicate that the expected changes of prolactin depression on seminal vesicle functions are obscured by the toxic effects of LHM. LHM treatment is therefore inappropriate for the study of prolactin depletion on the functions of the rat seminal vesicle.
Animals↗
[Effect of acute vitamin B1 deficiency caused by oxythiamine on protein biosynthesis in the spleen during immunogenesis].
Distinct increase in incorporation of 14C-protein hydrolysate of chlorella (5 microCi per an animal of 150 g body mass) into proteins of rat spleen was observed within 4 days after a single or repeated immunization of rats (180-200 g of body mass) with human blood serum gamma-immunoglobulin at a dose of 30-40 mg per 1 kg of animal mass. Under conditions of acute B1-avitaminosis caused by a single administration of hydroxythiamine at a high dose of 400 mg/kg incorporation of the label into spleen proteins of the immunized rats was decreased within 72 hrs. Thus, acute hydroxythiamine-produced B1-avitaminosis inhibited induction of protein biosynthesis stimulated during immunogenesis.
Acute Disease↗
Evidence that neutrophil accumulation induced by interleukin-1 requires both local protein biosynthesis and neutrophil CD18 antigen expression in vivo.
1. Mechanisms involved in neutrophil accumulation induced by intradermal injection of interleukin-1 (IL-1) in the rabbit were investigated using intravenously-injected 111In-labelled neutrophils. C5a des Arg, N-formyl-methionyl-leucyl-phenylalanine (FMLP) and leukotriene B4 (LTB4) were included for comparison. 2. Local inhibition of protein biosynthesis in the skin using actinomycin-D or cycloheximide blocked 111In-neutrophil accumulation induced by IL-1, but not that induced by the other mediators. 3. Actinomycin-D and cycloheximide had no effect on local plasma protein leakage induced by intradermally-injected C5a des Arg, or that induced by zymosan. 111In-neutrophil accumulation induced by zymosan was, however, partially suppressed. 4. A monoclonal antibody, MoAb 60.3, recognising neutrophil surface CD18 antigen, was preincubated with 111In-neutrophils before intravenous injection. This pretreatment did not affect circulating numbers of radiolabelled cells, but it inhibited their accumulation in response to IL-1, C5a des Arg and the other mediators. 5. The results suggest that neutrophil accumulation induced by IL-1, but not the other mediators, requires local protein biosynthesis, probably in the microvascular endothelium. Neutrophil accumulation to IL-1 and the other mediators appears to require neutrophil surface antigen, CD18. The inflammatory response to zymosan may be mediated by both endogenous C5a des Arg and IL-1.
Animals↗
Peptidyl-tRNA hydrolase and its critical role in protein biosynthesis.
Peptidyl-tRNA hydrolase (Pth) releases tRNA from peptidyl-tRNA by cleaving the ester bond between the peptide and the tRNA. Genetic analyses using Escherichia coli harbouring temperature-sensitive Pth have identified a number of translation factors involved in peptidyl-tRNA release. Accumulation of peptidyl-tRNA in the cells leads to depletion of aminoacyl-tRNA pools and halts protein biosynthesis. Thus, it is vital for cells to maintain Pth activity to deal with the pollution of peptidyl-tRNAs generated during the initiation, elongation and termination steps of protein biosynthesis. Interestingly, while eubacteria possess a single class of peptidyl-tRNA hydrolase, eukaryotes possess several such activities, making Pth a potential drug target to control eubacterial infections. This review discusses the aspects of Pth that relate to its history and biochemistry and its physiological connections with various cellular factors.
Carboxylic Ester Hydrolases↗
Effect of calcium antagonists on postischemic protein biosynthesis in gerbil brain.
BACKGROUND AND PURPOSE: Prolonged inhibition of protein synthesis precedes delayed neuronal death in the CA1 sector of the hippocampus after transient cerebral ischemia. Organic calcium antagonists have been recommended for alleviation of ischemic neuronal damage. The present study was undertaken to investigate whether these drugs improve the recovery of protein biosynthesis after interruption of cerebral blood flow. METHODS: Cerebral protein synthesis was measured biochemically and autoradiographically in gerbils submitted to 5 minutes of bilateral occlusion of the common carotid arteries followed by 2 hours or 2 days of recirculation. Flunarizine (25 mg/kg) or nimodipine (1.5 mg/kg) were applied intraperitoneally shortly after ischemia. RESULTS: Treatment with either calcium antagonist did not markedly influence postischemic recovery of protein synthesis in the resistant regions of the brain and did not prevent the persisting inhibition in the vulnerable stratum pyramidale of the CA1 sector of the hippocampus. CONCLUSIONS: The postischemic application of the organic calcium antagonists nimodipine and flunarizine does not promote postischemic recovery of protein synthesis. The beneficial effects of these drugs must, therefore, be based on other mechanisms.
Amino Acids↗
The specificity of protein biosynthesis.
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Protein Biosynthesis↗