Regulation of Synthesis of Non-Globin Proteins in Cell-free Extracts of Rabbit Reticulocytes

An optimized yeast cell-free lysate system for in vitro translation of human virus mRNA

Yeast (Saccharomyces cerevisiae) as a model organism has long been established to study various aspects of eukaryotic cellular and molecular biology. Cell-free lysates prepared from different yeast strains have been used as a powerful tool to study eukaryotic protein expression in vitro. Recently, we established a yeast cell-free lysate system for in vitro translation long and short L1 capsid gene mRNAs of human papillomavirus type 58. We were able to significantly improve the translation efficiencies of the viral mRNAs in the established system by optimizing the concentrations of potassium and magnesium and controlling the physiological status of the yeast cells used for lysate preparation. We proved that a single specific amino acid can be rate limiting for translation of a target mRNA. Here, we describe the materials, method, and technique used for the development of an efficient yeast cell-free translation system.

Hemin increases aerobic capacity of cultured regenerating skeletal myotubes

Regeneration of damaged, mature muscle occurs by differentiation of satellite cells. In culture, satellite cell myoblasts proliferate, align, and fuse to form cross-striated, contracting myotubes. The biochemical changes and the factors that regulate differentiation in satellite cells have not been investigated previously. We report here that no significant differences in glucose uptake rate or glucose oxidation rate were observed between regenerating myoblasts and myotubes, whereas the aerobic oxidation of palmitic acid increased 7.3-fold between these differentiation states. Specific activities of enzymes of critical importance in aerobic metabolism or in production of ATP were increased 2- to 3.5-fold during fusion. Addition of 20 microM hemin to regenerating muscle cultures potentiated the aerobic capacity as evidenced by a 23.6% increase in palmitate oxidation rate. Hemin also increased the specific activities of all nonheme enzymes investigated with the exception of phosphofructokinase. This augmentation of aerobic metabolism together with the time frame of active muscle differentiation suggests a complex role for hemin in myogenesis.

Iron deficiency in the elderly

Iron deficiency in the elderly almost always results from blood loss. The loss of iron can be viewed as occurring in four stages, which are reflected in the different tests used to diagnose iron deficiency. Tests used to diagnose iron deficiency have certain limitations regarding their ability to detect iron deficiency before the overt anaemia occurs. The tests which diagnose iron deficiency most accurately are low serum ferritin and reduced iron staining of a bone marrow aspirate. Because iron is present in many metabolic processes besides the production of haemoglobin, iron deficiency results in a variety of defects which are manifested at biochemical, tissue, and functional levels. Iron is a component of several enzymes in the respiratory electron transport chain. Adequate haem and iron levels are necessary to control cytoplasmic and mitochondrial protein synthesis. Iron deficiency results in tissue defects, including those affecting the gastrointestinal tract, and defects of mitochondria and lymphocytes. Normal iron levels seem to be necessary for normal work capacity. A deficiency of iron, independent of the anaemia, results in reduced exercise capacity that can be measured in both physiological and economic terms. Elderly patients complaining of increased fatigue should therefore be screened for iron deficiency. There is evidence to suggest that iron deficiency may predispose individuals to certain infections. Other information points to the promotion of certain bacterial and parasitic infections after rapid correction of iron deficiency. Thus elderly patients having iron replacement therapy should be followed closely. A deficiency of iron has been shown to result in certain behavioural and learning abnormalities. Iron deficiency has been shown to result in impaired control of body temperature, resulting in an increase in catecholamine levels. The impairment in heat-generating ability was shown to result from reduced conversion of T4 to T3 in the peripheral tissues.

CpA containing oligoribonucleotides specifically inhibit protein synthesis in rabbit reticulocytes

The diribonucleoside monophosphate CpA (and no others) inhibits polypeptide chain elongation in rabbit reticulocyte lysates at 10-50 microM. Furthermore, all the trinucleotides containing CpA, i.e., XpCpA and CpApX (X = U, C, A or G) block polypeptide chain elongation as well. At 10 microM the inhibition by XpCpA and not CpApX is transient because a 3'-exonucleolytic activity destroys the critical CpA moiety. The inhibitors do not appear to interfere with the aminoacylation of tRNAs or disrupt the interaction of amino-acyl-tRNAs with the protein synthetic machinery. High levels (200 microM) of CpA or the trinucleotides containing CpA have no effect on translation in a wheat germ cell-free system.

Interferon production in L929 cells under impaired translational conditions: comparison of rates of interferon, actin, Newcastle disease and encephalomyocarditis viruses mRNAs initiation of protein synthesis

The pattern of Interferon (IFN) production in virus-infected cells has been compared with the rate of bulk cellular protein synthesis, on one hand, and with the synthesis of representative cell and virus proteins such as actin, the gamma and the NP proteins of encephalomyocarditis (EMC) and Newcastle Disease (NDV) viruses, on the other hand. This was investigated under conditions of impaired protein synthesis such as i) high osmolarity media, ii) a virus-induced shut-off, and iii) in cells exposed to relatively low doses of cycloheximide (CXM), which slow elongation of protein chain and thus favour the translation of low-affinity messenger RNAs (mRNAs). In each instance IFN production was compared with 35S-methionine incorporation into TCA-precipitable materials and into SDS-polyacrylamide gel-analysed proteins. Data obtained from each of the experimental approaches all indicate that IFN production and cellular protein synthesis are modified in a closely related fashion suggesting that their mRNAs share a similar degree of affinity for ribosomes. Conversely, two mRNAs coding for representative EMC and NDV virus proteins exhibit, respectively, the highest and the lowest affinity for ribosomes as compared to actin mRNA.

Evidence that 2-allyl-2-isopropylacetamide and phenobarbital induce the same cytochrome P-450 in cultured chick embryo hepatocytes

The induction of cytochrome P-450 in cultured chick embryo hepatocytes was studied using two structurally unrelated compounds, 2-allyl-2-isopropylacetamide and phenobarbital. Pulse-labeling of these cells showed enhanced de novo synthesis of cytochrome P-450. The cytochrome induced by 2-allyl-2-isopropylacetamide, as well as the one induced by phenobarbital, reacted immunologically with antibodies raised against the major hepatic phenobarbital-induced isozyme. Additional form of cytochrome P-450 is induced exclusively by phenobarbital. These results clearly demonstrate that these two drugs induce at least one form of cytochrome P-450 in common.

Modulation of nonglobin mRNA levels in erythropoiesis

During erythropoiesis, the decrease of complexity of a RNA population is an important process as is globin mRNA accumulation. To determine the sequential control process of gene expression, many genomic clones which express in mouse reticulocytes were obtained and used for the titration of each mRNA level in the different stages of erythroid cells. The level of mRNAs of rt-clones decreases depending on the maturation of erythroid cells, and the coordinated and sequential control of this level is likely to be one of the factors affecting this process.

Functional deterioration of mouse liver ribosomes during aging: translational activity and activity for formation of the 47 S initiation complex

The translational activities of ribosomes from young and old mouse livers were examined in an assay system dependent on rabbit globin mRNA. Old ribosomes showed 30-40% lower activity than young ribosomes. This observation, together with our previous findings (N. Mori, D. Mizuno and S. Goto, Mech. Ageing Dev., 10 (1979) 379-398), suggests functional deterioration of ribosomes of old animals. To examine the mechanism of the deterioration, the activities for formation of the initiation complex of 40 S ribosomal subunits in the livers of young and old mice were examined in vitro. The activity was found to be 15-20% lower in old mice (21 months old or more) than in young ones. This fact partly explains the decreased activity for ribosomal protein synthesis in old mice.

Changes in tRNA levels during the induction of hemoglobin synthesis in Friend leukemia cells

There is a three- to four-fold decrease in the content/cell of tRNAs for ten different amino acids four days after the induction of erythroid differentiation in Friend leukemia cells, consistent with the decrease in cell volume that occurs. Surprisingly, there is an approximately two-fold increase in the cellular content of each of these tRNAs between day 4 and day 6 after induction, indicating the net synthesis of tRNA late in induction. The tRNA changes affect all species and do not result in tRNA specialization for hemoglobin synthesis, as occurs in normal erythroid development. The tRNA content of imidazole-treated cells, which do not synthesize hemoglobin although they undergo other changes of erythroid differentiation, decreases initially as described above, but shows no increase from day 4 to day 6.

The ubiquitin-mediated proteolytic pathway and mechanisms of energy-dependent intracellular protein degradation

In this review we briefly describe the lysosomal system, consider the evidence for multiplicity of protein degradation pathways in vivo, discuss in detail the ubiquitin-mediated pathway of intracellular ATP-dependent protein degradation, and also the possible significance of ubiquitin-histone conjugates in chromatin. For detailed discussions of the various characteristics and physiological roles of intracellular protein breakdown, the reader is referred to earlier reviews [1-7] and reports of recent symposia [8-10]. Information on the ubiquitin system prior to 1981 was described in an earlier review [11]. Hershko has briefly reviewed more recent information [12].

Stability of poly(A)(+)RNA in nucleate and anucleate cells of Acetabularia

The stability of poly(A)(+)RNA was compared in nucleate and anucleate cells of Acetabularia. While in the absence of the nucleus poly(A)(+)RNA exhibits a pronounced stability, it is significantly less stable in the presence of the nucleus.

Transfer RNA in reticulocyte maturation

The disappearance of tRNA during the maturation of rabbit reticulocytes under the stress of phenylhydrazine-induced hemolysis was studied. The tRNA content of reticulocytes and of erythrocytes derived from them was compared. The results show that tRNA persists longer after reticulocyte maturation than ribosomes and than the ability to incorporate amino acids into protein. Considerable uniformity of tRNA degradation was noted with about 15% of the tRNA for most amino acids remaining after reticulocyte maturation. The half-life of tRNA in the maturing cells is estimated to be 50--60 h. There is little tRNA lacking the 3'-terminal pCpCpA moiety in cells derived from reticulocytes.

Lodish model and regulation of ribosomal protein synthesis by insulin-deficient chick embryo fibroblasts

The production of ribosomal proteins in chick embryo fibroblasts that have been deprived of insulin is depressed in a much greater degree than that of most or all other cell proteins. Previous observations ruled out explanations for the preferential decrease in ribosomal protein formation that depend upon a selective destruction of ribosomal protein messages or a regulatory role for nascent ribosomal ribonucleic acid. The proposition has now been examined that ribosomal protein messenger ribonucleic acids (mRNAs) in the hormone-deficient chick embryo cells have a lower affinity for a limiting, early acting component of the initiating machinery than do most other cell messages and, in consequence, suffer from a translational disadvantage. The approach that was used depends upon the findings of Lodish and others that all mRNAs are not initiated with equal ease, that inhibitors of elongation favor the initiation of low-affinity mRNAs, and that agents that dampen an early step in initiation discriminate against the low-affinity messages. The idea was tested by comparing the effects of various inhibitors on the rates of synthesis of total cell protein and individual nonribosomal proteins, on the one hand, with those of individual ribosomal proteins, on the other. The results fit the Lodish model and are consistent with the conclusions that ribosomal protein mRNAs are more poorly initiated in the resulting fibroblasts than are most or all other cell messages and that this condition is largely or entirely responsible for the low rate of ribosomal protein formation.

Iron requirement for isolated rat liver mitochondrial protein synthesis

Isolated rat liver mitochondrial protein synthesis was severly inhibited by alpha, alpha-dipyridyl (a ferrous iron-chelating agent), chloramphenicol and hemin (10(-7) M or greater). In contrast, gamma, gamma-dipyridyl (a non-iron-chelating analogue of alpha, alpha-dipyridyl), cycloheximide and lower concentrations of hemin were non-inhibitory. The inhibitory action of alpha, alpha-dipyridyl was reversed by addition of Fe(NH4)2(SO4)2 while ZnCl2, CuCl2 and CoCl2 were ineffective. Hemin, however, did not protect against the alpha, alpha-dipyridyl inhibition of mitochondrial protein synthesis. These results indicate that ferrous iron is required for mitochondrial protein synthesis and suggests that it is through a mechanism independent of hemin concentration.

Synthesis of non-globin proteins in rabbit-erythroid cells. Synthesis of a lipoxygenase in reticulocytes

Peripheral rabbit reticulocytes synthesize at least 30 non-globin proteins. One of them is identified as a characteristic lipoxygenase on the basis of its molecular weight, its immunological properties and its behaviour on an ion-exchange column. The enzyme is not produced in bone marrow cells. The synthesis of the lipoxygenase in peripheral blood cells commences on the 3rd day of a bleeding anaemia, increases up to the 5th day and stays constant thereafter at least up to the 14th day. It is concluded that the appearence of the lipoxygenase, which plays a key role in the degradation of mitochondria in the course of maturation of reticulocytes to erythrocytes, is regulated at the translational level.

Synthesis of carbonic anhydrase in rabbit and chicken reticulocyte lysates

The synthesis of carbonic anhydrase, the second most abundant soluble protein of red blood cells, is shown to occur in rabbit and chicken reticulocyte lysates. This translation product was identified by chloroform/ethanol extraction, polyacrylamide gel electrophoresis in sodium dodecylsulphate and peptide mapping. In rabbit retic-locyte lysates, predominantly one of the two red cell isozymes, carbonic anhydrase I, is synthesised. The proportion of carbonic anhydrase synthesis (0.2-0.8% of total protein synthesis) in vitro is comparable to that (0.2-1.0%) in vivo for both rabbit and chicken reticulocytes.

The majority of calf muscle cell messenger RNAs contain poly(A)

Previous studies from our laboratory have investigated messenger RNA metabolism in calf muscle cells in tissue culture. The analysis of mRNA was based on its poly(A) content. We have now examined directly the proportion of mRNA which contains poly(A) in these cells. After separation of poly(A)+ -and poly(A) - -RNA on oligo(dT) -cellulos, the two fractions were translated in a reconstituted, heterologous cell-free protein-synthesizing system and the products were compared with those from the translation of total RNA. The great majority of mRNA form either prefusion or postfusion cultures was poly(A)- containing; quantitative determinations show that about 70-90% of the actin mRNA is poly(A)-containing. In order to determine if a large fraction of the calf muscle mRNA can be translated by a heterologous cell-free system, [3H]-POLY(A)+ -RNA was added to reticulocyte lysates and the formation of initiation complexes was followed. These experiments suggest that the bulk of calf muscle cell mRNA would be utilized in such a system and justify the use of cell-free systems to examine the poly(A) content of total mRNA. Thus, differential polyadenylation does not seem to be an important aspect of mRNA metabolism in cultured muscle cells. The previous study of mRNA in these cells, based on poly(A) content, is apparently a valid measure of overall mRNA metabolism.

Messenger RNA for myosin polypeptides: isolation from single myogenic cell cultures

Messenger RNA which stimilates the synthesis of myosin heavy chain in a reticulocyte lysate has been isolated from single myogenic cell cultures. Specific myosin polypeptides have been identified by immunoprecipitation with an antibody made to purified adult chicken skeletal muscle myosin. This mRNA binds to oligo(dT)-cellulose, and an active fraction from sucrose gradients migrates as 26S on formamide-polyacrylamide gels. The relative amount of this RNA increases dramatically at the time of terminal differentiation.

Protein synthesis in dystrophic muscle. Activity of the pH 5 supernatant fraction of muscle in dystrophic mice

The pH 5 supernatant fractions prepared from homogenates of tissues of normal and dystrophic mice were used to study the incorporation of [14C]phenylalanyl-tRNA into peptide. The incorpoation was markedly reduced using the muscle pH 5 supernatant fraction from dystrophic animals but no reduction was seen with brain, liver or heart preparations from dystrophic mice. The lower incorporation with dystrophic muscle pH 5 supernatant was not due to altered activity of ribonuclease, elongation factors, proteolytic enzymes, GTP or sulfhydryl reagents, but was attributable to the presence of activity that was inhibitory to protein synthesis.

Functional relationships between a reticulocyte polypeptide-chain-initiation factor (IF-MP) and the translational inhibitor involved in regulation of protein synthesis by haemin

The rate of initiation of protein synthesis in rabbit reticulocyte lysates is regulated by a translational inhibitor protein which is activated in the absence of added haemin. The effects of this inhibitor on amino acid incorporation are overcome by the protein synthesis initiation factor IF-MP which binds Met-tRNAf in a ternary complex with GTP and which can transfer this complex to small ribosomal subunits. Addition of this factor to haemin-deficient lysates prevents loss of polysomes and regenerates polysomes from 80-S single ribosomes, thus confirming an effect at the level of polypeptide initiation. The ability of the initiation factor to overcome the effects of various concentrations of the translational inhibitor suggests that the inhibitor inactivates the factor catalytically rather than stoichiometrically. In a system in vitro consisting of salt-washed 40-S ribosomal subunits, initiator Met-tRNAf and GTP, the initiation factor IF-MP transfers Met-tRNAf to the subunits in the absence of any other factor or mRNA. Equilibrium buoyant density gradient analysis in CsCl shows that formaldehyde-fixed subunits carrying Met-tRNAf bound under these conditions have a buoyant density approximately 0.02 g/cm3 lower than the bulk of salt-washed subunits, suggesting that approximately 100000 daltons of additional protein are associated with these subunits. This is in marked contrast to the amounts of protein bound to subunits incubated with Met-tRNAf and GTP in the presence of a crude ribosomal salt-wash fraction. The translational inhibitor has no effect on formation of the ternary complex IF-MP-Met-tRNAf-GTP but does impair the factor-catalysed transfer of Met-tRNAf to washed subunits. The possible mechanisms of action of the inhibitor on polypeptide chain initiation are reviewed in the light of these results.

Different lifetimes of reticulocyte messenger RNA

About 85-90% of cytoplasmic protein synthesized by young reticulocytes is globin, and about 10% is a polypeptide (I) of molecular weight 64,000 daltons. Maturation of reticulocytes is accompanied by selective reduction in the synthesis of polypeptide I, relative to globin; mature reticulocytes synthesize globin at a high level but make no detectable polypeptide I. Studies in which RNA from young and old reticulocytes was translated in a wheat germ cell-free extract showed that reduction in synthesis of polypeptide I was correlated with a reduction in the amount of translatable mRNA for this protein. Differential destruction of mRNA thus is an important factor in determining the types of proteins made during the final stages of erythropoiesis.

Globin synthesis in fibroblasts fused with erythroblasts. II. Human fibroblasts

Fusion of human (diploid) fibroblast monolayers with erythroblasts from 3-day chick embryos resulted in cultures containing on the average 14% heterokaryons and 8% fibroblast homokaryons. When these heterokaryon-containing cultures were labeled with radioactive amino acids during the first 24 h after fusion, the proportion of labeled proteins found in the globin region of analytical polyacrylamide gels showed a 40-fold increase compared with fibroblast homokaryons (0.08% vs. 4% of protein synthesized). Incorporation of radioactivity into globin decreased sharply during the second 24 h. Purified 35S-methionine-labeled globin from heterokaryon cultures gave rise to a tryptic fingerprint containing peptides characteristic of chick embryonic globins as late as 4 days after fusion. While fibroblasts in the fusion culture continue to go through the cell cycle normally, heterokaryons stop cycling almost completely soon after fusion.

Determination of secondary structure in rabbit globin messenger RNA by thermal denaturation

The secondary structure of highly purified globin messenger RNA has been investigated by alkaline hydrolysis, nuclease digestion, and thermal denaturation. The thermal denaturation properties of globin messenger have been compared to poly(U), poly (A), and a synthetic random sequence RNA copolymer. From these studies it is concluded that globin mRNA contains considerable secondary structure and that the amount of helical structure is greater than that which occurs with a random sequence polyribonucleotide. Globin mRNA contains, by comparison to the secondary structures of native DNA, tRNAs, or 18S rRNA, helices with involve 55-62% of the bases or 58-68% if a correction is made for the 3'-terminal poly(A) segment. The helices of globin mRNA appear to be unique as differences in the NaCl stabilization of this RNA have been noted when compared to other naturally ooccurring and synthetic RNAs. Comparison of the hyperchromicity maxima, obtained at 260 and 280 nm for globin mRNA and 18S rRNA, indicates that the helices of the two RNAs contain similar numbers of G-C base pairs. Differential analysis of NaCl stabilization curves indicate three discrete thermally denaturable helix types in globin mRNA.