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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Expression of recombinant proteins in bacteria has facilitated the characterization of many gene products. However, the biochemical characterization of recombinant proteins is limited since the bacterially expressed proteins are often synthesized as fusion polypeptides. The presence of bacterial sequences in fusion proteins further limits the use of these proteins for generating antibodies since the bacterial sequences are also antigenic. We describe two new bacterial expression vectors based on the pATH series of plasmids. These vectors were made by precisely deleting all of the trpE coding sequences found in pATH. The new vectors have enabled us to express eukaryotic genes as nonfusion polypeptides. These altered plasmids can be used to insert any DNA sequence of interest through a multiple cloning site located just 3' of an ATG start codon. Protein expression is still under the control of the trp operon and is carried out at great efficiency when the bacteria are tryptophan deprived. Studies presented here test the expression system with neurofilament subunits, NF-L and NF-H. Large amounts of recombinant nonfusion proteins were produced. Also, a time course of induction shows that the production of the nonfusion proteins was under the control of the trp operon which is readily inducible after tryptophan starvation and addition of indoleacrylic acid. These vectors may be useful for the overexpression of many proteins in a form closely approximating their native state.
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PMID:A new series of trpE vectors that enable high expression of nonfusion proteins in bacteria. 142 8

A nucleotide sequence identical with that of the recently identified murine pancreatic ribonuclease (RNAase) was isolated from a murine spleen cDNA library. Active RNAase was expressed and secreted from Escherichia coli lon-htpr- transformed with a plasmid containing the E. coli trp promoter followed by the murine RNAase gene sequence, including the original eukaryotic 26-amino-acid signal sequence. Approx. 1 mg of properly matured RNAase protein/litre was secreted into the medium of a fermentor culture after the promotor was induced by tryptophan starvation. When the signal sequence was deleted from the plasmid, intracellular RNAase activity was very low and there was no significant supernatant RNAase activity. Even higher RNAase yields were obtained with a synthetic gene for bovine pancreatic ribonuclease cloned after the signal sequence of the murine gene. About 2 mg of correctly processed RNAase A/litre was isolated from the growth medium, and a further 8-10 mg of correctly processed RNAase/litre could be isolated from the soluble fraction of the cells. Thus this eukaryotic signal sequence is both recognized by the E. coli transport and processing apparatus and gives efficient secretion, as well as export, of active, mature mammalian RNAases.
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PMID:Secretion of mammalian ribonucleases from Escherichia coli using the signal sequence of murine spleen ribonuclease. 156 61

The sensitivity and resistance of six human melanoma cell lines to gamma-interferon (gamma-IFN) and tumour necrosis factor-alpha (TNF-alpha) have been examined. Amelanotic cell lines were more sensitive to gamma-IFN and TNF-alpha than melanotic cells. The cytotoxicity of gamma-IFN and TNF-alpha could be reversed in all cells by the addition of L- or D-tryptophan to the culture medium. Melanoma cells resistant to gamma-IFN excrete calcium activated neutral protease (CANP) and as a consequence, make L-tryptophan available by the hydrolysis of serum proteins in the culture medium. Resistance to gamma-IFN could be reversed by the addition of specific CANP inhibitor, whereas gamma-IFN-sensitive strains became more resistant with the addition of CANP to the culture medium. It has been confirmed that gamma-IFN induces indoleamine 2,3-dioxygenase in melanoma cells. This enzyme utilizes the superoxide anion (O2-) as a substrate for the oxidation of either L- or D-tryptophan to N-formylkynurenic acid leading to cell death. The induction of this degradative pathway for L-tryptophan kills cells by starvation of this essential and relatively scarce amino acid. TNF-alpha induces manganese-containing superoxide dismutase (MnSOD) which also uses O2- to produce cytotoxic concentrations of hydrogen peroxide. Therefore, it can be concluded that the cytotoxicity of both gamma-IFN and TNF-alpha depends on the availability of L-tryptophan as the substrate for the removal of O2- via indoleamine 2,3-dioxygenase.
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PMID:Tryptophan protects human melanoma cells against gamma-interferon and tumour necrosis factor-alpha: a unifying mechanism of action. 166 25

In vitro transcription studies with a trp leader DNA template derived from a double deletion mutant of Serratia marcescens revealed that the transcription complex pauses synthesis of part of the RNA antiterminator, structure 2:3. Pausing was enhanced by NusA protein and was dependent on the concentration of UTP in the transcription reaction mixture. A weak antiterminator pause also was detected during transcription of the wild-type S. marcescens trp leader template in the presence of NusA protein and 1 microM UTP. Transcription pausing following synthesis of the antiterminator also was observed in a cell-free transcription-translation system. Antiterminator-induced pausing may play an important role in vivo by delaying synthesis of RNA segment 4. This delay may influence basal level control in cells with an excess of tryptophan. In addition, formation of the antiterminator pause structure may introduce a more stringent tryptophan starvation requirement for RNA polymerase to read through the attenuator.
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PMID:The RNA antiterminator causes transcription pausing in the leader region of the tryptophan operon. 169 Jul 21

We have previously reported a series of biological events in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-intoxicated rats which resulted in elevated brain serotonin (5-HT) levels, offering a possible explanation of the acute toxicity (reduced feed intake and death) in these animals. It was thus hypothesized that depletion of central 5-HT stores should alter the TCDD-induced starvation syndrome. Brain 5-HT was selectively depleted by intracerebroventricular infusions of the neurotoxin 5,7-dihydroxytrytamine (5,7-DHT). Subsequently the animals were given a lethal dose of TCDD. In rats treated with 5,7-DHT hypothalamic 5-HT was depleted up to 90% compared to control animals, yet TCDD induced the expected reduction of bodyweight and feed intake. These results suggest that although TCDD increases central 5-HT levels as a result of increased plasma tryptophan, this may not be the main cause for reduced feed intake and lethality in these animals.
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PMID:Depletion of brain serotonin does not alter 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced starvation syndrome in the rat. 175 37

Toxoplasma gondii invaded and proliferated in cultured human umbilical vein endothelial cells. Preincubation of the human umbilical vein endothelial cells with human rIFN-gamma induced a high degree of inhibition of T. gondii replication, with the effect being dose dependent. In order to try to elucidate the inhibitory mechanism, we tested the presence of several factors that are known to operate against intracellular parasites in other cell types. We found, by means of a competitive inhibitor, that L-arginine-dependent production of reactive nitrogen intermediates was not the cause of inhibition of T. gondii proliferation, thus contrasting with the inhibitory mechanism found in activated mouse macrophages. Furthermore, the inhibition of replication was not overcome by oxygen scavengers or by saturation of the system with tryptophan, suggesting that neither reactive oxygen intermediates nor the induction of tryptophan starvation was responsible.
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PMID:Human endothelial cells are activated by IFN-gamma to inhibit Toxoplasma gondii replication. Inhibition is due to a different mechanism from that existing in mouse macrophages and human fibroblasts. 190 38

The present study investigated the involvement of corticotrophin-releasing factor (CRF) in the thermogenic and anorexic actions of serotonin (5-HT) in the rat. Serotonergic compounds and CRF antibody were injected directly into the third ventricle of conscious, male Sprague-Dawley rats. Thermogenesis was measured as changes in whole body oxygen consumption by indirect calorimetry. Central injections of 5-HT (0.5-50 micrograms, i.c.v.) significantly increased resting oxygen consumption (VO2; maximum 12.5% increase), without obvious effects on behaviour. Similar increases in VO2 (12-17%) were observed following central injections of the 5-HT precursors, tryptophan (14 micrograms, i.c.v.) or 5-hydroxytryptophan (5-HTP, 20 micrograms, i.c.v.), and peripheral (10 mg/kg, i.p.) or central (30 micrograms, i.c.v.) injections of the 5-HT reuptake inhibitor, DL-fenfluramine. Administration of a polyclonal CRF antibody (3 microliters, i.c.v.) 10 min prior to serotonergic compounds, significantly reduced (77-106%) the increases in VO2 observed in response to central injections of 5-HTP (20 micrograms), 5-HT (50 micrograms) or peripheral injections of fenfluramine, but not those observed in response to either 30 micrograms fenfluramine (i.c.v.) or 20 micrograms 5-HT. Voluntary food intake was measured for 6 h in rats following 16 h starvation. Six-hour food intake was significantly reduced (30-60%) in rats given central injections of 5-HT or 5-HTP, and central or peripheral injections of fenfluramine.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Involvement of corticotrophin releasing factor (CRF) in the thermogenic and anorexic actions of serotonin (5-HT) and related compounds. 193 36

This review focuses on the gene-enzyme relationships and the regulation of different levels of the aromatic amino acid biosynthetic pathway in a simple eukaryotic system, the unicellular yeast Saccharomyces cerevisiae. Most reactions of this branched pathway are common to all organisms which are able to synthesize tryptophan, phenylalanine, and tyrosine. The current knowledge about the two main control mechanisms of the yeast aromatic amino acid biosynthesis is reviewed. (i) At the transcriptional level, most structural genes are regulated by the transcriptional activator GCN4, the regulator of the general amino acid control network, which couples transcriptional derepression to amino acid starvation of numerous structural genes in multiple amino acid biosynthetic pathways. (ii) At the enzyme level, the carbon flow is controlled mainly by modulating the enzyme activities at the first step of the pathway and at the branch points by feedback action of the three aromatic amino acid end products. Implications of these findings for the relationship of S. cerevisiae to prokaryotic as well as to higher eukaryotic organisms and for general regulatory mechanisms occurring in a living cell such as initiation of transcription, enzyme regulation, and the regulation of a metabolic branch point are discussed.
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PMID:Aromatic amino acid biosynthesis in the yeast Saccharomyces cerevisiae: a model system for the regulation of a eukaryotic biosynthetic pathway. 194 92

The cephalic gustatory stimuli during a meal yield nutritional information and aid in the efficient control of homeostasis. This study was focused on either appetite for flavored food or feeding behavior in growing male Sprague-Dawley rats under various states of protein nutrition. In fasted rats, endogenous protein degradation was suppressed by ingestion of glucose that was sufficient to meet energy needs. The decrease in the amount of diet intake was compensated by sugar ingestion, except for sucrose. Rats that ingested sucrose exceeded 115% of total energy intake, compared to ingestion of saccharin as a control. Appetite and meal size are primarily dependent upon the dietary protein level, whether it was beyond normal requirements or not and, thus, flavoring by certain taste material is effective for a diet sufficient in protein, but not for a deficient one. In addition, rats fed a diet containing amino acids preferred saccharin and monosodium L-glutamate (MSG) and grew normally. But, when L-tryptophan-deficient diet was offered, the preference for tryptophan was elicited, and then MSG intake was elevated and their growth became normal. However, preference for saccharin never occurred because the level of tryptophan in blood fluctuated and was not maintained within normal limits. The strong preference for sweetness that is evoked by starvation is directly regulated by the negative energy balance. The animals' primary concern was energy intake and their second concern was protein nutrition, regardless of flavoring.
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PMID:Appetite and taste preference in growing rats given various levels of protein nutrition. 195 39

We have examined the effects of changing the length and codon content of the trp leader peptide coding region on expression of the trp operon of Escherichia coli, it had previously been shown that coupling of transcription and translation in the trp leader region is essential for both basal level control and tryptophan starvation control of transcription attenuation in this operon. We have found that increasing the length of the leader peptide coding region by 55 codons allowed normal basal level control and normal tryptophan starvation control. As expected, the presence of a nonsense codon early in the leader peptide coding region decreased basal expression and eliminated starvation control. Introducing tandem rare codons had no effect on basal level expression, but eliminated the tryptophan starvation response. Frameshifting at tandem rare codons was tested as the most likely explanation for loss of the tryptophan starvation response, but the results were inconclusive.
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PMID:The effects of leader peptide sequence and length on attenuation control of the trp operon of E.coli. 201 62


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