Preferential regulation of protein synthesis initiation complex formation by purine nucleotides

Adult male volunteers with a prior history of either moderate (N = 12) or heavy (N = 14) marihuana use were systematically observed before, during and after a 21-day period of free access to 1 g 2% delta-9 THC marihuana cigarettes. A matched sample of casual alcohol drinkers (N = 11) served as a control group. Sleep and other molar behaviors were observed hourly to obtain a representative sample of daily activity. Both moderate and heavy users were less active immediately after marihuana use and slept more on days following heavier consumption. Heavy users reduced their waking activity on days following heavier consumption, as well as during the entire period of marihuana availability. These reactions did not persist beyond the period of availability for either group. The findings suggest a dose-related delayed reaction to heavy marihuana consumption which disappears following the cessation of regular use. However, changes in activity following single doses of marihuana may be related more to the social circumstances of its use than to its pharmacological action.     

Dependence of timing of mitotic events on the rate of protein synthesis and DNA replication in sea urchin early cleavages

To understand what processes affect the cell-cycle timing of mitotic events in early cleavage cycles of sea urchin embryos, a study was made on the effects of (a) reducing protein synthesis with emetine and (b) DNA replication with aphidicolin, on the timing of nuclear envelope breakdown, anaphase onset and cytokinesis. When protein synthesis was slightly inhibited by administration of emetine, the delay in the mitotic events increased, with an increase in the delay in accumulation of proteins up to the levels to which cells must synthesize the proteins to execute the cleavage. This indicated that protein synthesis affects the timing of mitotic events. The delay in cleavage cycles caused by a slight inhibition of DNA replication with aphidicolin was in proportion to the concentration of aphidicolin administered, suggesting that DNA replication also affects the timing of mitotic events. Furthermore, it was confirmed that accumulation of the proteins to the levels required for execution of the first cleavage precedes completion of DNA replication as a requirement for execution of the first cleavage. These results imply the existence of process(es) affected by protein synthesis that are included in a feedback control system which prevents the initiation of mitosis until after the completion of DNA replication; it is the characteristic of a cell-cycle control system that has been predicted theoretically.     

Inhibition of protein synthesis by zinc: comparison between protein synthesis and RNA synthesis

Inhalation of zinc fumes may lead to the acute respiratory distress syndrome. The mechanisms of pulmonary zinc toxicity are not yet understood. Therefore we investigated zinc-dependent depression of protein and RNA synthesis in rat and human lung cell lines. 1. After exposure to 120 or 150 micromol/l zinc, RNA synthesis as assessed by uridine incorporation decreased by 60-70% between 0 and 2 h exposition in rat alveolar type II cells (L2 cells) and human fibroblast-like cells (11Lu and 16Lu cells), and by 90% between 0 and 4 h in carcinoma-derived cells (A549 cells). 2. After 2 h exposure, L2, 11Lu, and 16Lu cells were half-maximally inhibited by 50 micromol/l zinc, whereas A549 cells were more resistant with half-maximal inhibition at 100 micromol/zinc. 3. Protein and RNA synthesis was inhibited in parallel in L2, 11Lu, and A549 cells as indicated by simultaneous determination of uridine and amino acid incorporation. In 16Lu cells, the decline in protein synthesis preceded RNA synthesis inhibition. Pretreatment with RNA synthesis inhibitors (amanitin or actinomycin D) had no effect on time curve and intensity of RNA synthesis inhibition. Taken together, our results indicate that the suppression of RNA and protein synthesis likely are independent phenomena, due to direct zinc effects on these biosynthetic pathways.     

Binding constants in the formation of mammalian protein synthesis initiation complexes and the role of mRNA

Acute idiopathic thrombocytopaenic purpura is the most common of the thrombocytopaenias of childhood. Clinically it is associated with petechiae, mucocutaneous bleeding and occasionally haemorrhage into tissues. The oral mucosa is frequently involved. This paper describes a case presenting in general dental practice.     

Chemical protein synthesis

Chemical protein synthesis is a field in transition. Previously, the synthetic accomplishment itself was the major focus of work in this field. Increasingly, chemical synthesis is now being applied to understanding how biological function originates in the structure of the protein molecule. A novel approach--'chemical ligation', which is the chemoselective reaction of unprotected peptide segments in water at pH7--has made the total synthesis of proteins a robust and practical route to the study of structure-function relationships. For certain protein families, chemical protein synthesis is the most effective way to obtain functional proteins direct from genome sequence data.     

Effects of trypsin on protein synthesis in macrophages

1. Integrated electromyogram (e.m.g.) from the vastus lateralis muscles, and steady-state rates of oxygen uptake, were measured simultaneously during the performance of set rates of positive (concentric) and negative (eccentric) work at 50 rev/min on a motorized bicycle ergometer. 2. Similar experiments were also carried out at other pedalling rates and using other leg muscles. 3. The relationships between each of the variables (integrated e.m.g., oxygen consumption) and mean torque on pedals were found to be linear (r greater than 0-98) with a remarkable degree of reproducibility in surface e.m.g. for each subject over several months. 4. The ratio of the e.m.g. slopes at 50 rev/min (positive/negative) was 1-96 +/- 0-12 while the same ratio for the oxygen uptake slopes was 6-34 +/- 0-82. The discrepancy between the ratios suggests that not only is less muscle fibre activity required to maintain the same exerted force during negative work exercise, but there is also a substantial reduction in the oxygen uptake when the fibres are stretched. This was observed for all speeds of pedalling.     

The formation of protein disulphide bonds

Transgenic tobacco plants have been obtained expressing nucleoprotein (N) gene sequences of three different tospoviruses known to affect vegetable crops: tomato spotted wilt virus (TSWV), tomato chlorotic spot virus (TCSV), and groundnut ringspot virus (GRSV). The chimeric plant transformation vector used comprised the three viral N gene sequences, each with a copy of the CaMV 35S promoter and the nos terminator. Despite the high levels of homology between the different N gene sequences (74-82%) and the presence of repeated promoter and terminator sequences in this construct, unrearranged copies of this triple N gene construct were stably maintained in both Escherichia coli and Agrobacterium tumefaciens plasmids used during the cloning process, as well as in several generations of transgenic tobacco plants. A transgenic tobacco line was obtained that exhibited high levels of resistance to all three tospoviruses, showing the possibility of producing transgenic plants with a broad resistance to tospoviruses by introducing tandemly cloned viral N gene sequences. DNA analysis of this transgenic plant line shows that the multivirus resistance trait is confined to a single genetic locus, which is very convenient for further breeding purposes.     

Impact of protein deprivation on protein and DNA synthesis in the developing rat pancreas

The metabolic effects of protein malnutrition on growth and development of the exocrine pancreas are largely unknown. The aim of the present study was to evaluate the effects of protein malnutrition on pancreatic protein and DNA synthesis during postnatal development. Rat dams and their offspring were fed a protein-deficient diet (6% casein) or a control diet (25% casein) during gestation, lactation and after weaning. Pancreatic protein and DNA synthesis were measured in vitro at postnatal ages 1, 3, 10, 23, 36 and 60 days, by assessing [3H]leucine and [3H]thymidine incorporation in freshly isolated acini. Different patterns of protein synthesis were seen in the two groups. At birth, pancreatic protein synthesis was low in both control and malnourished animals. At day 3, protein synthesis in the control acini increased 10-fold while synthesis in acini of the malnourished animal group was only 50% of age-matched control values. No differences in protein synthesis were detected between the control and malnourished groups between 10 and 36 days of age. At 60 days (adulthood), acinar protein synthesis declined in the control-fed rats, but a significant increase was observed in the malnourished animals (p < 0. 0005). At birth, DNA synthesis was high in the acini from both control and malnourished animals. The low-protein diet induced a slight reduction in DNA synthesis at day 3, without altering the general pattern during later stages of development. In conclusion, protein deprivation has variable effects on pancreatic protein and DNA synthesis at different stages of postnatal development. Furthermore, the mechanisms of control within acini appear to be intrinsically regulated.     

Effect of lithium on structure formation of graphite-like boron nitride with carbothermal synthesis

Formation of a graphite-like boron nitride structure during carbothermal analysis in the presence of lithium compounds in a stream of nitrogen or ammonia is studied by electron microscopy, x-ray, and chemical methods. A marked reduction in the formation temperature for graphite-like boron nitride with a highly ordered structure is observed and chemical aspects of the process are discussed.Institute of Problems of Materials Science, National Academy of Sciencesof the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 1–8, July–August, 1994.     

Malaria circumsporozoite protein inhibits protein synthesis in mammalian cells

Native Plasmodium circumsporozoite (CS) protein, translocated by sporozoites into the cytosol of host cells, as well as recombinant CS constructs introduced into the cytoplasm by liposome fusion or transient transfection, all lead to inhibition of protein synthesis in mammalian cells. The following findings suggest that this inhibition of translation is caused by a binding of the CS protein to ribosomes. (i) The distribution of native CS protein translocated by sporozoites into the cytoplasm as well as microinjected recombinant CS protein suggests association with ribosomes. (ii) Recombinant CS protein binds to RNase-sensitive sites on rough microsomes. (iii) Synthetic peptides representing the conserved regions I and II-plus of the P.falciparum CS protein displace recombinant CS protein from rough microsomes with dissociation constants in the nanomolar range. (iv) Synthetic peptides representing region I from the P.falciparum CS protein and region II-plus from the P.falciparum, P.berghei or P.vivax CS protein inhibit in vitro translation. We propose that Plasmodium manipulates hepatocyte protein synthesis to meet the requirements of a rapidly developing schizont. Since macrophages appear to be particularly sensitive to the presence of CS protein in the cytosol, inhibition of translation may represent a novel immune evasion mechanism of Plasmodium.     

The origin of protein synthesis: on some molecular fossils identified through comparison of protein sequences

Sequence data, even if only marginally significant, and evolutionary arguments suggest that a similarity may exist between class II aminoacyl-tRNA synthetases and proteins involved in the nonribosomal biosynthesis of peptide antibiotics, and more in general, those belonging to the family of adenylate-forming enzymes. If correct, this hypothesis of homology may imply that the first peptide syntheses might have occurred on phosphopantetheine molecules in a thioester world and/or on a variant of the coenzyme A (CoA) in an RNA world. Therefore, peptide synthesis probably evolved on tRNA-like molecules from the CoA (or a variant CoA molecule) that had the potential for nucleotide extension, that made possible the evolution to the current mechanism of protein synthesis. Our hypothesis on the existence of such homology implies that a series of evolutionary steps such as the existence of a primitive catalytic domain with poor substrate specificity towards both (amino acids + ATP + pre-CoA (and/or CoA)) and (amino acids + ATP + tRNA-like) molecules may have occurred. Therefore, the pre-CoA (and/or CoA) and the tRNA-like molecules were able to use this enzyme ambiguity for a certain period, thus giving weight to the scheme of evolutionary transitions mentioned above.     

How antibiotics work: protein synthesis

1. Antibiotics are important agents for the treatment of infections. 2. They are special chemicals produced by a few species of microorganisms which inhibit the growth of other micro-organisms. 3. They inhibit growth by attacking one of five sensitive sites. 4. A selection of antibiotics attacking the protein synthesis mechanism are identified and their modes of action described.     

Effect of glutamine on protein synthesis in isolated intestinal epithelial cells

The purpose of this study was to determine the etiologic factors of denture stomatitis. Fifteen subjects with clinical evidence of localized simple denture stomatitis, fifteen subjects without clinical signs of denture stomatitis, and forty-five subjects with clinical evidence of generalized simple denture stomatitis were investigated clinically and mycologically. Subjects were evaluated according to age, sex, duration of denture usage, smoking habits, frequency of denture brushing, overnight denture wearing, pH level of saliva and degree of candidal colonization and candidal formation. Salivary samples and swabs were taken from the palate and the mucosal surfaces of the dentures investigated mycologically in order to identify the yeast colonies. Smears were taken from the palate and investigated in order to identify candidal formation. No statistically significant relationship was found between denture stomatitis and age, sex, duration of denture usage, frequency of denture brushing, overnight denture wearing or pH level of saliva. There was however, a statistically significant relationship between denture stomatitis and denture hygiene, smoking habits, candidal colonization and candidal formation.