Polyamines are necessary for maximum in vitro synthesis of globin peptides and play a role in chain initiation

Importance of potassium ions for ribosome structure and function revealed by long-wavelength X-ray diffraction

The ribosome, the largest RNA-containing macromolecular machinery in cells, requires metal ions not only to maintain its three-dimensional fold but also to perform protein synthesis. Despite the vast biochemical data regarding the importance of metal ions for efficient protein synthesis and the increasing number of ribosome structures solved by X-ray crystallography or cryo-electron microscopy, the assignment of metal ions within the ribosome remains elusive due to methodological limitations. Here we present extensive experimental data on the potassium composition and environment in two structures of functional ribosome complexes obtained by measurement of the potassium anomalous signal at the K-edge, derived from long-wavelength X-ray diffraction data. We elucidate the role of potassium ions in protein synthesis at the three-dimensional level, most notably, in the environment of the ribosome functional decoding and peptidyl transferase centers. Our data expand the fundamental knowledge of the mechanism of ribosome function and structural integrity.

Roles of polyamines in translation

Polyamines are organic polycations that bind to a variety of cellular molecules, including nucleic acids. Within cells, polyamines contribute to both the efficiency and fidelity of protein synthesis. In addition to directly acting on the translation apparatus to stimulate protein synthesis, the polyamine spermidine serves as a precursor for the essential post-translational modification of the eukaryotic translation factor 5A (eIF5A), which is required for synthesis of proteins containing problematic amino acid sequence motifs, including polyproline tracts, and for termination of translation. The impact of polyamines on translation is highlighted by autoregulation of the translation of mRNAs encoding key metabolic and regulatory proteins in the polyamine biosynthesis pathway, including S-adenosylmethionine decarboxylase (AdoMetDC), antizyme (OAZ), and antizyme inhibitor 1 (AZIN1). Here, we highlight the roles of polyamines in general translation and also in the translational regulation of polyamine biosynthesis.

Decrease in the S1 protein of 30-S ribosomal subunits in polyamine-requiring mutants of Escherichia coli grown in the absence of polyamines

The reason for the decrease of polypeptide-synthetic activity of 30-S ribosomal subunits obtained from two polyamine-requiring mutants of Escherichia coli, grown in the absence of polyamines, has been studied by analyzing the total and split proteins of 30-S subunits by disc gel and slab gel electrophoresis. It was concluded that the decrease of S1 protein in 30-S subunits was responsible for the decrease of polypeptide synthesis in polyamine-requiring mutants of E. coli grown in the absence of polyamines.

Effects of osmolarity, ions and compatible osmolytes on cell-free protein synthesis

To mimic what might happen in cells exposed to hypertonicity, the effects of increased osmolarity and ionic strength on cell-free protein synthesis have been examined. Translation of globin mRNA by rabbit reticulocyte lysate decreased by 30-60% when osmolality was increased from 0.35 to 0.53 osmol/kg of water by the addition of NaCl, KCl, CH(3)CO(2)Na or CH(3)CO(2)K. In contrast, equivalent additions of the compatible osmolytes betaine or myo -inositol caused a 40-50% increase in the rate of translation, whereas amino acids (50-135 mM) that are transported via system A had no significant effect. Addition of 75 mM KCl caused a dramatic fall in the amount of the 43 S pre-initiation complex, whereas it was totally preserved when osmolarity was similarly increased by the addition of 150 mM betaine. The formation of a non-enzymic initiation complex between rabbit [(3)H]Phe-tRNA, poly(U) and the 80 S ribosomes was unaffected by the addition of 75 mM NaCl or KCl, but translation of the complex decreased by 70%. Density-gradient centrifugation of reticulocyte extracts translating endogenous mRNA revealed that addition of 150 mM betaine had no effect, whereas addition of 75 mM KCl caused a marked decrease in the polysome peak, concomitant with an increase in the proportion of 80 S ribosomes and ribosomal subunits, even when elongation was inhibited with fragment A of diphtheria toxin. These results are consistent with the notion that both initiation and elongation are inhibited by unusually high concentrations of inorganic ions, but not by the compatible osmolytes betaine or myo -inositol.

Immunoelectron microscopic study for polyamines

The polyamines (PAs) are ubiquitous polycationic metabolites in eukaryotic and prokaryotic cells and are believed to be intimately involved in the regulation of DNA, RNA, and protein biosynthesis, the exact function of which remains unclear, mainly because of a lack of knowledge of PA subcellular localization. In this study, using immunoelectron microscopy, we have demonstrated that PAs are predominantly located on free and attached ribosomes of the rough endoplasmic reticulum in the neurons of the lateral reticular nucleus of rat medulla oblongata. The nuclei, axons, and nerve endings were devoid of PA. This suggests that PAs are one of the components of biologically active ribosomes, being closely involved in the translation processes of protein biosynthesis.

A highly efficient cell-free protein synthesis system from Escherichia coli

We modified a cell-free coupled transcription/translation system from Escherichia coli with the T7 phage RNA polymerase, and achieved a productivity as high as 0.4 mg protein/ml reaction mixture. First, we found that the optimal concentrations of phosphoenolpyruvate and poly(ethylene glycol) are interdependent; higher concentrations of the former should be used at higher concentrations of the latter. Second, the use of a condensed 30000 x g cell extract, in place of the conventional one, significantly increased the initial rate of protein synthesis. This phenomenon was demonstrated to be due to a reason other than elimination of inhibitory molecule(s) from the extract. For this system with the condensed extract, the phosphoenolpyruvate and poly(ethylene glycol) concentrations were again co-optimized, resulting in production of chloramphenicol acetyltransferase at a productivity of 0.3 mg/ml. Finally, the productivity was further increased up to 0.4 mg/ml, by supplementation of the pool of amino acids. This improved cell-free protein synthesis system is superior in productivity to any other cell-free systems reported so far, including the continuous-flow cell-free system.

The importance of dietary polyamines in cell regeneration and growth

The polyamines putrescine, spermidine and spermine are essential for cell renewal and, therefore, are needed to keep the body healthy. It was previously believed that polyamines are synthesized by every cell in the body when required. However, in the present paper evidence is provided to show that, as in the case of the essential amino acids, the diet can supply sufficient amounts of polyamines to support cell renewal and growth. Systematic analysis of different foods was carried out and from the data obtained, the average daily polyamine consumption of British adults was calculated to be in the range 350-500 mumol/person per d. The major sources of putrescine were fruit, cheese and non-green vegetables. All foods contributed similar amounts of spermidine to the diet, although levels were generally higher in green vegetables. Meat was the richest source of spermine. However, only a part of the polyamines supplied by the diet is available for use by the body. Based on experiments with rats it was established that polyamines were readily taken up from the gut lumen, probably by passive diffusion, and were partly metabolized during the process of absorption. More than 80% of the putrescine was converted to other polyamines and non-polyamine metabolites, mostly to amino acids. The enzyme responsible for controlling the bioavailability of putrescine was diamine oxidase (EC 1.4.3.6). For spermidine and spermine, however, about 70-80% of the intragastrically intubated dose remained in the original form. Considering the limitations on bioavailability (metabolism and conversion), the amounts of polyamines supplied by the average daily diet in Britain should satisfy metabolic requirements.

Bimodal action of spermine on ribosomal peptidyltransferase at low concentration of magnesium ions

At 6 mM Mg2+, submillimolar concentrations of spermine affect the end-point as well as the kinetic phase of puromycin reaction in a cell-free system from Escherichia coli. When the ternary complex AcPhe-tRNA-poly(U)-ribosome (complex C) is formed in the absence of ribosomal wash (FWR fraction), the final degree of AcPhe-puromycin synthesis is raised from 12% to 60%, as the concentration of spermine increases from zero to 200 microM. However, spermine displays partial noncompetitive inhibition at the kinetic phase of the reaction. The inhibitory effect of spermine is related with its binding to AcPhe-tRNA. When complex C is formed in the presence of FWR fraction, spermine slightly affects the final degree of puromycin synthesis is markedly stimulated by the addition of relatively low concentrations of spermine. Kinetic analysis of the activation phase revealed that spermine attached on a specific site of complex C, acts as a nonessential, partial noncompetitive activator. The stimulatory effect of spermine seems to be due to its interaction with ribosomes. Further additions of spermine cause partial noncompetitive inhibition on the puromycin reaction. This result suggests that complex C possesses a second binding site, responsible for the inhibitory effect of spermine. Both activator and inhibitor sites can be occupied by spermine at the same time.

Some properties of a partially purified inhibitor of protein synthesis isolated from bovine cornea

Bovine cornea extracted with 0.154 M NaCl yielded a protein fraction which (i) inhibited protein synthesis in rabbit reticulocyte lysates, and (ii) reduced the incorporation of formyl-methionine from f[35S]Met-tRNA(f) into polypeptides. The inhibition was reversed by millimolar concentrations of glucose 6-phosphate or cAMP and partially reversed by the addition of initiation factor eIF-2. Thus, the corneal inhibitor may act by directly interfering with the activity of eIF-2.

Requirements for the inactivation of ribosomes by gelonin

Inactivation of Artemia salina and rabbit ribosomes by gelonin requires ATP and a high-Mr factor present in the rabbit reticulocyte-lysate post-ribosomal supernatant. The kinetic constants of the gelonin-catalysed release of adenine from A. salina ribosomes are Km = 4.35 microM and Kcat. = 0.1 min-1 in the absence of cofactors, and Km = 1.15 microM and Kcat. = 108 min-1 in their presence. The last two values are similar to those measured for ricin A chain in the absence of cofactors (Km = 2.02 microM and Kcat. = 317 min-1).

Concentration-dependent effects of natural polyamines on peptide chain initiation and elongation in a cell-free system of protein synthesis

Spermidine and spermine at submillimolar concentrations stimulate the rate of incorporation of amino acid into protein in a cell-free system, directed either by endogenous or exogenous mRNA (TMV, globin). The stimulatory effects of these polyamines are exerted at both the stages of initiation and elogation and are more pronounced in the case of TMV or globin mRNA, amounting to approximately 2.3-fold stimulation over the polyamine-free system. The number of polysomes and the polysome-associated radioactivity increase approximately 2-fold in the presence of spermine. Synthesis of large polypeptides is a characteristic feature of the stimulatory event. However, elevated concentrations of spermidine and spermine strongly inhibit amino acid incorporation into protein. Inhibition is manifest at the stage of peptide elongation. In the case of endogenous mRNA the addition of an excess of polyamines results in a non uniform inhibition of amino acid incorporation. A most interesting finding is that, with increasing concentrations of polyamines, the intensity of four bands with Mr values of 63000, 44000, 15500 and 12500 respectively, increases or leastwise remains constant while others fade, indicating differential translation of proteins in the presence of polyamines.

Subunit association defects in Escherichia coli ribosome mutants lacking proteins S20 and L11

The subunit association capacity of 30S and 50S ribosomal subunits from Escherichia coli mutants lacking protein S20 or L11 as well as of 50S subunits depleted of L7/L12 was tested by sucrose gradient centrifugation and by a nitrocellulose filtration method based on the protection from hydrolysis with peptidyl-tRNA hydrolase of ribosome-bound AcPhe-tRNA. It was found that the subunits lacking either S20 or L11 display an altered association capacity, while the 50S subunits lacking L7/L12 have normal association behavior. The association of S20-lacking 30S subunits is quantitatively reduced, especially at low Mg2+ concentrations (5-12 mM), and produces loosely interacting particles which dissociate during sucrose gradient centrifugation. The association of L11-lacking 50S subunits is quantitatively near-normal at all Mg2+ concentrations and produces loosely associating particles only at low Mg2+ concentrations (5-8 mM); the mechanism of their association with 30S subunits, however, or the structure of the resulting 30S-50S couples is altered in such a way as to cause the ejection of an AcPhe-tRNA molecule pre-bound to the 30S subunits in response to poly(U).

Polyamines inhibit the ATP-dependent proteolytic pathway in rabbit reticulocyte lysates

Reticulocytes contain a soluble nonlysosomal proteolytic pathway that requires ATP and ubiquitin. Polyamines at physiological concentrations were found to inhibit rapidly the ATP-dependent proteolytic system in reticulocyte lysates; spermidine and putrescine inhibited this process by 26-72% and spermine by 71-96%. Spermine had little effect on the ATP-independent breakdown of oxidant-treated hemoglobin. By fractionating the ATP-dependent system, we show that polyamines inhibit the ATP-dependent degradation of ubiquitin-protein conjugates.

Polyamine cytochemistry: comparisons between cytochemical, autoradiographic, immunocytochemical and chemical results in the prostate

Results obtained with two newly developed fluorescence cytochemical methods for detecting the polyamines spermidine and spermine have been compared to autoradiographic localization of biosynthetically labelled polyamines, to immunocytochemical results obtained with antibodies directed against spermidine and spermine, and to chemical polyamine determinations using the rat prostate as a model tissue. Complete agreement between all five methods was obtained. Application of perchloric acid to formaldehyde-fixed sections of rat prostate strongly reduced the o-phthalaldehyde inducible and formaldehyde-fluorescamine inducible fluorescence characteristic of spermidine and spermine. Perchloric acid extracted 40% of tissue-bound polyamines from formaldehyde-fixed tissue sections, and molecules with the physicochemical characteristics of polyamines constituted 80-90% of all fluorescamine reactive molecules extracted. Our results therefore confirm the specificity of the o-phthalaldehyde and formaldehyde-fluorescamine methods for polyamine cytochemistry. As polyamines are strongly implicated in cellular growth regulation and cancer, simple and inexpensive techniques for polyamine histochemistry may be useful for interpreting the biological and pathophysiological roles of these molecules.

Ribosomal protein phosphorylation induced during Q fever or by lipopolysaccharide: in vitro translation is stimulated by infected liver ribosomes

Q fever, as well as the lipopolysaccharide prepared from the rickettsial agent Coxiella burnetii, stimulates the phosphorylation of guinea pig liver ribosomal protein S6. In vitro mRNA and ribosome-dependent rabbit reticulocyte lysate translation systems reconstituted with ribosomes and mRNAs from infected animal livers were more active than those with mRNAs and ribosomes from uninfected animals. Treatment of ribosomes with a ribosomal supernatant phosphatase reduced the in vitro translation activities; the largest decreases occurred in systems with ribosomes and mRNAs from infected liver. These experiments provide a basis for explaining the increased hepatic protein synthesis during Q fever and demonstrate, perhaps for the first time, the phosphorylation of ribosomal protein in response to lipopolysaccharide. The implications of these observations are discussed in the context of previous studies on stimulated transcription and translation during Q fever.

Optimisation of protein synthesis rates in reticulocyte lysates and reconstituted systems

Means of increasing the very low activity of a reconstituted protein synthesising system from rabbit reticulocytes were investigated. Increasing the concentration of labelled amino acid, addition of polyamines, use of Sepharose-filtered as opposed to centrifuged ribosomes, use of untreated as opposed to gel-filtered cytosol and an increase in ratio of cytosol to ribosomes all contributed to the increase in activity of the system to the point where activity was clearly consistent with initiation taking place. Similar activities could not be attained with rat liver cytosol though rat liver ribosomes incorporated well in reticulocyte cytosol. Incorporation by lysates was also found to be dependent on the concentration of the labelled amino acid added.

Differential inhibition of protein synthesis: a possible biochemical mechanism of thalidomide teratogenesis

A theory concerning the chemical and biochemical mechanisms of thalidomide teratogenesis is presented. A considerable body of evidence suggests that the glutarimide ring of thalidomide may exert its biological activity because of its resemblance to the imide pyrimidines thymine and uracil. In addition to the glutarimide ring, thalidomide contains a moderately reactive phthalimide moiety, which allows the spontaneous formation of various glutarimide derivatives in fetal tissues. A model is proposed in which the phthalimide group reacts with small nucleophiles, most likely the polyamines, to produce a derivative(s) having a similar biochemical potential to that of cycloheximide, a glutarimide which is a powerful inhibitor of the elongation phase of protein synthesis. Interference in the elongation phase results in the selective inhibition of the translation of messages which have a high translational efficiency. Evidence is reviewed concerning the differential inhibition or protein synthesis by cycloheximide and the effects of this inhibition on various biochemical and biological processes which are critical during development and differentiation. A similar biochemical activity by the putative thalidomide derivative(s) could explain its extreme teratogenic potential. A number of parallels between the biological effects of thalidomide and cycloheximide are discussed which support the idea that a similar biochemical activity is involved. The theory readily explains many of the observed biological effects of thalidomide including the large difference between fetal and adult toxicity. In addition, evidence is reviewed which suggests that the teratogenic properties of a number of drugs which are structurally related to thalidomide may have a common chemical basis due to the similarity of their imide core structures to thymine and uracil.

Preferential stimulation of the in vivo synthesis of a protein by polyamines in Escherichia coli: purification and properties of the specific protein

The possibility that polyamines can stimulate the synthesis of special kinds of proteins has been examined by using a polyamine-requiring mutant of Escherichia coli. It was found that the synthesis of some proteins, particularly one with a molecular weight (Mr) of 62K, was significantly stimulated following polyamine supplementation of polyamine-starved cells. The preferential stimulation of the synthesis of this polyamine-induced protein of Mr 62K (PI protein) was followed by the stimulation of overall protein synthesis by polyamines. PI protein was purified to homogeneity and some of its properties were examined. From studies on the effect of PI protein on MS2 RNA directed protein synthesis, it was shown that this protein stimulated the synthesis of RNA replicase by 2.2-fold in the presence of 1 mM spermidine.

Modulation of protein synthesis in a cell-free system derived from rat brain by corticotropin (ACTH), magnesium, and spermine

Modulation of protein synthesis by fragments of the ACTH molecule has been studied in a cell-free system obtained from subcortical brain tissue of rats. Both the activity of the protein-synthesizing system and its sensitivity to ACTH-like peptides appeared to be highly dependent on the Mg2+ and spermine concentrations. At optimal Mg2+ concentrations (4 mM) the peptide sequences ACTH(1-24) and (11-24) were both inhibitory, the latter being the more active. The inhibitory effect was reduced or abolished at higher (suboptimal) concMg2+ concentrations. Spermine, like ACTH, inhibited protein synthesis at the optimal Mg2+ concentration. However, at lower Mg2+ concentrations spermine had a stimulatory effect and maximal activity was obtained at 0.75-1.0 mM Mg2+. In the presence of spermine (60 microM) and Mg2+ (0.75 mM), a half-maximal inhibition of protein synthesis was obtained with a peptide concentration of 5 microM. A structure-activity study showed that the peptides ACTH(7-16)-NH2, (11-24), (5-18, 17Lys 18Lys)-NH2 and (15-24) were active in inhibiting protein synthesis, whereas the fragments ACTH(1-16)-NH2 and (17-24) were inactive. The results are discussed in terms of an interaction between ACTH, Mg2+, and spermine, and intracellular processes involved in protein synthesis.

Differential stimulation by polyamines of phage DNA-directed in vitro synthesis of proteins

The effect of polyamines on T7- and lambda rifd18 DNA-directed synthesis of proteins in an Escherichia coli cell-free system has been studied. When T7 DNA was used as a template, the degree of stimulation by spermidine of protein synthesis was larger with T7 RNA polymerase than with Mr 42 K protein, while the synthesis of Mr 13.5 K protein was not stimulated significantly by spermidine. The synthesis of T7 RNA polymerase was stimulated approx. 10-fold by 1 mM spermidine. When lambda rifd18 DNA was used as a template, the synthesis of beta beta' subunits of RNA polymerase was stimulated greatly by spermidine, while the synthesis of elongation factor Tu and ribosomal proteins was not stimulated significantly by spermidine. Spermidine stimulation of T7 DNA-directed synthesis of T7 RNA polymerase was at the level of both translation and transcription. The degree of stimulation by spermidine was greater at the level of translation. Putrescine stimulated the synthesis of T7 RNA polymerase and Mr 42 K protein to a small degree at the level of translation.

The study of spermidine-stimulated polypeptide synthesis in cell-free translation of mRNA from lactating mouse mammary gland

The stimulatory effect of spermidine on the translation of poly(A)+ mRNA from lactating mouse mammary glands in a wheat germ system was studied. Spermidine stimulated total polypeptide synthesis about 2.5-fold relative to that occurring in the presence of an optimal concentration of Mg2+ alone. The size and the number of polysomes were about 1.6-times larger in the presence of spermidine than in its absence. A similar magnitude of increase in peptide chain initiation, 1.4-fold, was found when the extent of peptide chain initiation was measured by determining the residual polypeptide synthesis subsequent to the addition of inhibitor(s) of peptide chain initiation to the in vitro translation system with or without spermidine at various times of the incubation. Time-course study of the release of polypeptide from polysomes showed that spermidine stimulated this process to a much greater extent than peptide chain initiation, indicating that the polyamine also increases the rate of peptide chain elongation. The extent of stimulation of peptide chain elongation by spermidine was estimated to be about 1.5-fold when the disappearance of isotope-labeled nascent peptides from polysomes was measured by pulse-chase experiments. These results indicate that spermidine stimulates the cell-free translation of mammary mRNA by increasing the rates of both initiation and elongation of polypeptide synthesis to almost the same extent. The polyamine also reduced the relative amount of incomplete polypeptides, thereby increasing the yield of full-length translational products.

Phosphorylation of troponin and myosin light chain by cAMP-independent casein kinase-2 from rabbit skeletal muscle

Casein kinase-2 from rabbit skeletal muscle was found to phosphorylate, in addition to glycogen synthase, troponin from skeletal muscle, and myosin light chain from smooth muscle. Troponin T and the 20,000 Mr myosin light chain are phosphorylated by casein kinase-2 at much greater rates than glycogen synthase. The V values for the phosphorylation of troponin and myosin light chain are nearly an order of magnitude greater than that of glycogen synthase; however, the Km values for these two substrates are greater than that for glycogen synthase. The kinase activities with the various protein substrates are stimulated approximately three- and fivefold by 5 mM spermidine and 3 mM spermine, respectively. Heparin is a potent inhibitor of the kinase when casein, glycogen synthase, or myosin light chain is the substrate. However, with troponin as substrate the kinase is relatively insensitive to inhibition by heparin. The amount of heparin required for 50% inhibition with troponin as substrate is at least 10 times greater than with casein as substrate. The phosphorylation of troponin by casein kinase-2 results in the incorporation of phosphate into two major tryptic peptides, which are different from those phosphorylated by casein kinase-1. The site in myosin light chain phosphorylated by casein kinase-2 is different from that phosphorylated by myosin light chain kinase.

Polyamine requirement for efficient translation of amber codons in vivo

Multiplication of several amber mutants of bacteriophage T7 was decreased in two polyamine-deficient mutants of Escherichia coli K-12 carrying amber suppressors, relative to the multiplication of wild type bacteriophage T7 in the same hosts. In contrast the same T7 amber bacteriophages multiplied well in these strains when supplemented with polyamines. The requirement for polyamines for optimal translation of amber codons in vivo was confirmed by showing that infection of polyamine-depleted E. coli with bacteriophage T7 carrying an amber mutation in gene 1 resulted in an increased accumulation of the amber fragment of the gene 1 protein and a decreased accumulation of the full-length gene 1 protein compared with infection of an amine-supplemented culture. These results indicate that one important function of polyamines in vivo is concerned with protein translation and the protein-synthesizing ribosomal complex.

Increase of fidelity of polypeptide synthesis by spermidine in eukaryotic cell-free systems

The mechanism of spermidine-induced increase of fidelity of polypeptide synthesis in a wheat germ cell-free system has been studied. It was found that the increase of fidelity in the presence of spermidine occurred mainly at the level of binding of aminoacyl-tRNA to ribosomes, that reduction of misreading was more marked at the 5'-base than at the 3'-base of the codon and that misreading caused by paromomycin and kanamycin C was not significantly decreased by spermidine. It was deduced from these results that spermidine inhibited low-frequency misreading more strongly than high-frequency misreading. In addition, spermidine was found to stimulate the rejection of non-cognate aminoacyl-tRNA mainly at an initial discrimination step during the binding of amino-acyl-tRNA to ribosomes, and slightly at a subsequent GTP-dependent discrimination step, the so-called proofreading step. In yeast, rabbit reticulocyte, and Artemia salina cell-free systems, spermidine was found to increase the fidelity of protein synthesis.

Association of spermine and 4S RNA during axonal transport in regenerating optic nerves of goldfish

Experiments were designed to determine whether polyamines are bound to 4S RNA and then transported axonally along regenerating optic axons of goldfish. In one set of experiments, inhibition of retinal RNA synthesis by intraocular injections of 10 microgram of cordycepin, blocked the axonal transport of both [3H]RNA and [14C]spermidine by about 65%, 6 and 14 days after injection. Intraocular injections of vinblastine, (0.1, 0.5 or 1.0 microgram) an agent which interrupts axonal transport of proteins, had no effect on retinal RNA synthesis nor on the amount of [14C]spermidine incorporated into the TCA-insoluble fraction of retinal extracts. However, the axonal transport of both [3H]RNA and [14C]polyamines was affected in a dose-dependent fashion; the inhibition of both was approximately 80% at the higher dose. Further evidence for an association between axonally transported 4S RNA and polyamines came from experiments in which regenerating optic axons were cut and allowed to degenerate 6 days after injection of [3H]spermidine into the eye. The loss of optic axons from the tectum 7 days after cutting the nerve resulted in an 86% loss of TCA insoluble polyamines, indicating a largely intra-axonal locus. A similar loss of 4S RNA was found in identical experiments following injections of [3H]uridine into the eye. Finally, experiments were performed in which [3H]spermidine was injected into both eyes of 12 fish whose optic nerves had been regenerating for 18 days. Six days later, fish were sacrificed and RNA was extracted from tectal homogenates by hot phenol and ethanol precipitation. The major stable RNA species were separated by SDS-polyacrylamide disc gel electrophoresis and radioactivity was determined by extraction of 2.0 mm gel slices. Results showed co-migration of 3H with 4S RNA optical density peaks, and not with 28S and 18S ribosomal RNA peaks, suggesting that some polyamine-associated radioactivity is bound to axonally transported 4S RNA. When the nature of that radioactivity was determined on an amino acid analyzer, it was found to be present primarily as spermine and not as the injected compound spermidine. The data are consistent with the hypothesis that some spermine is bound to 4S RNA and then axonally transported along regenerating axons of the goldfish optic nerve.

Polyamines inhibit the protein kinase 380--catalyzed phosphorylation of eukaryotic initiation factor 2 alpha

Polyamines putrescine, spermidine, and spermine specifically inhibit the PK 380--catalyzed phosphorylation of eukaryotic initiation factor 2 alpha (eIF-2 alpha). Since te PK 380--dependent phosphorylation of eIF-2 alpha inhibits the initiation or protein synthesis, the possibility exists that the polyamines enhance protein synthesis by inhibiting the phosphorylation of eIF-2 alpha by PK 380.

Differential stimulation by polyamines of phage RNA-directed synthesis of proteins

The effect of polyamines on Q beta and MS2 phage RNA-directed synthesis of three kinds of protein in an Escherichia coli cell-free system has been studied. With both phage RNAs, the degree of stimulation of protein synthesis by spermidine was in the order RNA replicase greater than A protein, while the synthesis of coat protein was not stimulated significantly by spermidine. The synthesis of RNA replicase was stimulated by 1 mM spermidine approx. 8-fold. From the results of Q beta RNA direct alanyl-tRNA and seryl-tRNA binding to ribosomes and initiation dipeptide synthesis, it is suggested that the preferential stimulation of the synthesis of RNA replicase by spermidine is due at least partially to the stimulation of the initiation of RNA replicase synthesis.

Speed-accuracy relationships during in vitro and in vivo protein biosynthesis

Poly U-directed incorporation of phenylalanine and leucine into polypeptide has been described in at least 50 papers since 1961. In general, high translation activities are associated with high accuracies, and vice-versa. Moreover, a vast body of independent experimental data (effect of ethanol, temperature, urea, aminoglycosides, etc... on protein synthesis) put together here suggests that, in many circumstances, speed and accuracy of elongation are correlated. This result is to be contrasted with the view that the speed and the fidelity of protein synthesis are two opposing parameters. In this report, recent experimental data on the nature and effect of ribosomal ambiguity (ram) and streptomycin resistance (Strr) mutations are reexamined. Models on the action of streptomycin and other misreading-inducing antibiotics, as well as long-standing ideas on the control of misreading in mammalian systems are critically evaluated. An explanation is provided for the long-befuddling data on the action of gentamicin.

Relationship between methylation of adenine near the 3' end of 16-S ribosomal RNA and the activity of 30-S ribosomal subunits

The relationship between methylation of adenine near the 3' end of 16-S ribosomal RNA and the activity of 30-S ribosomal subunits has been studied using 30-S subunits from kasugamycin-sensitive and kasugamycin-resistant bacteria. Analysis of the proteins of 30-S subunits by gel electrophoresis showed that the content of protein S1 in 30-S subunits from a kasugamycin-resistant strain was smaller than that in 30-S subunits from the parent strain. Although polyphenylalanine-synthetic activity of 30-S subunits from a kasugamycin-resistant strain previously methylated by a methylase purified from Escherichia Q13 was nearly equal to that of untreated 30-S subunits, both phenylalanine-synthetic activity and the content of protein S1 in the 30-S particles reconstituted from 23-S core particles and split proteins from the kasugamycin-resistant strain increased by prior methylation of 23-S core particles by the methylase. These results suggest that methylation of adenine near the 3' end of 16-S rRNA induces an increase of polypeptide-synthetic activity by the acceleration of binding of protein S1 to S1-depleted 30-S subunits.

Regulation of prenatal and postnatal protein synthesis in mouse brain

Regulation of protein synthesis during prenatal and postnatal brain development was examined using postmitochondrial supernatant (PMS) fractions and isolated ribosome-pH 5 enzyme systems from fetal, neonatal, and adult neural tissue. The rate of polyuridylic acid (poly-U)-dependent protein synthetic activity was inversely proportional to the endogenous rate of protein synthesis in either the PMS fractions or ribosomal preparations. A careful analysis of the kinetics of the poly-U-dependent polypeptide synthesis revealed that there was a lag in the time at which certain of the PMS preparations could begin to utilize the poly-U template as sole source of mRNA. The lag period was dependent upon the developmental age of the neural tissue used and the Mg2+ concentration of the protein synthesis reaction. Since previous work reported that the observed developmental decrease in the rate of polypeptide synthesis utilizing a poly-U template could not be measured by several isolation techniques to determine if the purification procedure might have affected the ribosomes in some manner by removing a specific protein(s) involved in ribosome-cytosol interactions. At 6 mM-Mg2+ the rate of poly-U-dependent protein synthesis was inversely proportional to the rate of endogenous synthesis and depended upon the method used to isolate the ribosomes: microsomes congruent to Triton X-100-treated < DOC-treated < KCl-treated. However, there was no age-dependent effect with any of the ribosomal preparations. The data suggest that there is a developmental modulating effect of ribosomal activity in PMS preparations which is not found in association with the isolated ribosome-pH 5 enzyme protein synthesizing system.

Effect of polyamines on cell-free protein synthesizing systems from rat cerebral cortex, cerebellum and liver

The naturally occurring polyamines spermine and spermidine stimulate in low concentrations the amino acid-incorporating activity of cell-free systems from cerebral cortex, cerebellum and liver from the rat to a significant degree, but in high concentrations they have strong inhibiting effects on these systems. Maximal polyamine stimulation is observed with suboptimal Mg2+ concentrations in the reaction mixtures; increasing Mg2+ to 15 mM results in an inhibition of cell-free protein synthesis by polyamines even at low concentrations. The stimulating effect of spermine and spermidine involves a facilitated binding of template RNA and aminoacylated tRNA to the ribosomes. In contrast, the aminoacylation of tRNA is not influenced. These data indicate that spermine as well as spermidine have regulatory functions during the translational process in cerebral cortex, cerebellum and liver. They seem to interact with ribosomal functions and to cause a shift in the optimal Mg2+ concentration required for the synthesis of brain and liver proteins.

An improved and easy technique for polyamine determination in biological samples. Application to cell-free system from hypertrophied rat heart

An accurate, improved cation-exchange chromatographic method using o-phthalaldehyde and ultraviolet detection at 280 nm for the determination of free polyamines (putrescine, spermidine, spermine) has been developed. Different samples, such as the 105,000 g supernatant of reticulocyte or heart muscle, and KCl ribosomal wash containing initiation factors, can be analysed. The minor modification of reagents results in a good precision and sensitivity, which is demonstrated by a relative standard deviation of 5--9% and recoveries of 98%. This technique is of particular interest because it allows polyamine determination in biological samples with high concentrations of salt.

Defect in the split proteins of 30-S ribosomal subunits and under-methylation of 16-S ribosomal RNA in a polyamine-requiring mutant of Escherichia coli grown in the absence of polyamines

Polyphenylalanine synthesis was carried out with Escherichia coli Q13 50-S ribosomal subunits and reconstituted 30-S particles containing different combinations of 23-S core particles and 30-S subunit split proteins obtained from a polyamine-requiring mutant of E. coli during its growth in the presence or absence of putrescine. It was concluded that the defect in the amount of some kinds of 30-S subunit split proteins was responsible for the decrease of polypeptide synthesis in a polyamine-requiring mutant of E. coli grown in the absence of polyamines. The methylation of 16-S RNA during growth in the absence of putrescine was decreased, while the degree of methylation of 23-S RNA did not change significantly. The decrease in methylation of 16-S RNA in the absence of putrescine was due mainly to a decrease of methylation of adenine. The relationship between the decrease of polypeptide synthetic activity of 30-S ribosomal subunits obtained from a polyamine-requiring mutant of E. coli grown in the absence of polyamines and the decrease of methylation of 16-S RNA is discussed.