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

The correlation between protein synthesis and the nuclear division cycle in Neurospora crassa hyphae was studied by inhibiting protein accumulation by two different experimental procedures: (1) starvation for lysine in a lysine-requiring mutant (lys-1); and (2) addition of cycloheximide. Lysine starvation in a lys-1 strain of N. crassa quickly blocked the nuclear division cycle and nuclei accumulated in G1 phase, as judged by their DNA content. After re-addition of lysine to starved cultures, a discontinuous pattern of uridine incorporation into DNA can be seen, showing that the nuclei were well synchronized. On the other hand, treatment with cycloheximide caused the arrest of a large proportion of the nuclei, also, in the G2 phase of the cell cycle. These results indicate that inhibition of protein synthesis may have multiple effects on the cell cycle in N. crassa and that, while moderate inhibition specifically blocks nuclei at a regulatory point in late G1, strong or complete inhibition demonstrates requirement for protein synthesis at other points in the cycle that are not necessarily regulatory points.
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PMID:Control points in Neurospora crassa nuclear division cycle: different effects of the inhibition of protein accumulation. 622 4

Further studies on the expression of the two aspartokinase activities in Bacillus bovis are presented. Aspartokinase I (previously shown to be inhibited and repressed by lysine) was found to be repressed by diaminopimelate in the wild-type strain. However, in a mutant unable to convert diaminopimelate to lysine, starvation for lysine resulted in an increase in aspartokinase I activity. Thus, lysine itself or an immediate metabolite was the true effector of repression. Aspartokinase II (previously shown to be inhibited by lysine plus threonine) was repressed by threonine. Studies with the parent strain and auxotrophs inidicated that only threonine or an immediate metabolite of threonine was involved in this repression. Methionine and isoleucine were not effectors of any of the detected aspartokinase activities. Apart from inhibition and repression controls, a third as yet undefined regulatory mechanism operated to decrease the levels of both aspartokinases as growth declined, even in mutants in which repression control was absent. In thiosine-resistant, lysine-excreting mutants with elevated levels of aspartokinase, the increase in activity could always be attributed to one enzyme or the other, never both. The existence of separate structural genes for each aspartokinase is therefore suggested.
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PMID:Regulation of lysine- and lysine-plus-threonine-inhibitable aspartokinases in Bacillus brevis. 624 20

The nucleotide sequence of the yeast gene TRP5 and its 5' and 3' flanking regions was determined. The deduced coding sequence for tryptophan synthase contains 2,127 base pairs. The protein chain has a calculated molecular weight of 76,544. Yeast tryptophan synthase, a bifunctional protein, has a primary structure which corresponds to an Escherichia coli tryptophan synthase alpha chain-beta chain fusion. An NH2-terminal 239 amino acid segment of yeast tryptophan synthase is homologous with E. coli tryptophan synthase alpha subunit, while a distal 389 amino acid residue segment is homologous to the E. coli tryptophan synthase beta chain. This order of segments of the yeast enzyme is the reverse of the chromosomal order characteristic of all prokaryotes that have been examined. The two segments are joined by a connecting region of 28 residues in the yeast enzyme which is not homologous to either the alpha or beta chains of the bacterial enzyme. A portion of the connecting region of yeast tryptophan synthase exhibits nucleotide sequence similarity to the 3' terminus of E. coli trpC and the trpC-trpB intercistronic region. Active site cysteine, histidine, and lysine residues in the beta 2 subunit of E. coli tryptophan synthase are conserved in the yeast enzyme. Also conserved in the yeast enzyme are 6/8 amino acid residues having an important role in maintaining the structure and function of the E. coli tryptophan synthase alpha subunit. S1 nuclease mapping was used to identify three major mRNA transcripts with different 5' termini. Potential T-A-T-A sites for transcription initiation were identified, as well as other sequences that occur frequently in yeast genes. A 5' flanking region of TRP5 was shown by DNA/DNA hybridization to be present in multiple copies in the yeast genome. TRP5 mRNA levels, measured by RNA/DNA hybridization, increased 2- to 7-fold in response to starvation for either tryptophan or histidine, indicating transcriptional regulation.
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PMID:Yeast gene TRP5: structure, function, regulation. 627 87

Basal-level misreading of asparagine codons was examined in a number of Escherichia coli strains. Lysine substitutions were measured by quantitating the amount of charge heterogeneity in MS2 coat protein. In most strains the heterogeneity was consistent with misreading of AAU codons at a frequency of 3-6 X 10(-3). Strains with streptomycin resistance mutations (rpsL) have reduced levels of misreading. There is no significant difference in the frequency of basal-level errors in stringent (relA+) and relaxed (relA) strains, even during starvation for amino acids unrelated to the substitution being studied.
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PMID:Control of basal-level codon misreading in Escherichia coli. 637 72

Measurement of protein synthesis in individual organs is important in understanding metabolic changes in injury, sepsis, or starvation. Methods, mostly isotopic, for measuring synthesis are plagued by problems of experimental design and interpretation. Thus it is desirable to use a variety of methods based on different assumptions. The present study is the first to isolate radioactive aminoacyl-tRNA in the study of protein synthesis in muscle and skin. Male rats, 200-300 g, trained to eat chow for 4 hr/day were studied at 2 hr (absorptive) or 16 hr (postabsorptive) after a meal. Under ether anesthesia, a tracer dose of L-[4-5-3H(N)]-lysine was infused at a constant rate. At 20, 30, or 40 min 1 ml of arterial blood was withdrawn and 2-g samples of skin and thigh muscle were quickly excised and frozen. Samples were pooled from 4 to 7 rats for each infusion period. Concentrations and specific activities were determined for plasma lysine, and for free, tRNA, and protein-bound lysine in muscle and skin. Protein renewal rates in absorptive and postabsorptive periods averaged 6 and 9% per day in muscle, and 20 and 35% in skin. The data for muscle confirms results of other methods and suggests little contribution of rapidly turning over protein. The contribution of skin to whole body protein synthesis, about 500 mg . 100 g-1 . day-1, is similar in magnitude to the contributions of muscle, liver, or intestine.
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PMID:Protein synthesis rates in rat muscle and skin based on Lysyl-tRNA radioactivity. 640 30

Lysine-mediated inhibition of postexponential growth in Saccharomyces cerevisiae occurred when glucose, fructose, or maltose, but not lactate, pyruvate, or ethanol, was used as the carbon source. Arginine starvation is not responsible for the inhibitory effect, since neither the intracellular pool of glucose-grown (inhibited) cells nor that of lactate-grown (noninhibited) cells contained arginine.
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PMID:Effect of carbon source on lysine-mediated inhibition of postexponential growth of Saccharomyces cerevisiae. 640 82

Various tumor cells contain chromatographically distinct isoacceptor tRNA species. To decide whether the tumor-specific species represent an expression of a separate tRNA gene or only an undermodified form of normal tRNAPhe, nucleotide sequences of tRNAPhe isolated from neuroblastoma and normal mouse liver were determined by postlabeling techniques. The results showed identical sequences except for the changes of post-transcriptional modifications in the anticodon loop. Normal mouse liver tRNAPhe contained Cm32, Gm34, and the hypermodified YOH next to the 3' end of the anticodon. On the contrary, tRNAPhe from neuroblastoma contained C32, G34, and, instead of YOH base m1G. A small proportion of tRNAPhe species contained an undermodified YOH base. For the examination of the conditions leading to the undermodified tRNAPhe, Vero cells derived from the kidney of African green monkey in culture were used. In these cells, deprivation of methionine or lysine resulted in changes in tRNAPhe modification similar to those in tumor cells. Ehrlich ascites tumor cells were examined to determine whether the presence of altered tRNAPhe species in various tumors is also the result of starvation of some nutritional factors. Results obtained with these cells showed that tRNAPhe species lacking the Y base disappeared in tumor-bearing mice after intraperitoneal injection with a mixture of amino acids and vitamins. Thus it is concluded that tumor-specific tRNAPhe species are the products of aberrant post-transcriptional modification, not the transcripts of different, normally repressed genes.
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PMID:Alterations in post-transcriptional modification of the Y base in phenylalanine tRNA from tumor cells. 640 57

Starvation of the polyamine-dependent Chinese-hamster ovary cells for ornithine or ornithine-derived polyamines in serum-free culture resulted in the formation of cadaverine and its aminopropyl derivatives, N-(3-aminopropyl)cadaverine and NN'-bis(3-aminopropyl)cadaverine. The synthesis of these unusual amines was inhibited by treatment of the cells with DL-2-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17). In the absence of ornithine (the normal substrate), ornithine decarboxylase thus appeared to catalyse the decarboxylation of lysine to cadaverine. Cell proliferation was markedly inhibited by ornithine deprivation of the cells, and further depressed by exposure of the cultures to difluoromethylornithine.
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PMID:Polyamine starvation causes accumulation of cadaverine and its derivatives in a polyamine-dependent strain of Chinese-hamster ovary cells. 640 84

This paper describes experiments in which we have investigated the mechanism by which amino acid starvation regulates the initiation of protein synthesis in mammalian cells. We have examined the ability of a range of lysine analogues to stimulate protein synthesis in lysine-deprived mouse Ehrlich ascites tumour cells in culture. Of those analogues tested, only those which are cleaved to lysine intracellularly are capable of restoring protein synthesis to the level seen in fully fed cells. Lysine which is covalently linked to agarose does not stimulate translation. After 5 min incubation of lysine-deprived cells with the analogue lysine p-nitroanilide, the lysine concentration in cell extracts is restored to that found in extracts from fed cells, and protein synthesis is maximally stimulated within 5-10 min. During this period of time there is no increase in the concentration of lysine in the medium. These data indicate that it is the size of the intracellular rather than the extracellular amino acid pool which regulates the rate of protein synthesis during amino acid deprivation.
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PMID:Stimulation of protein synthesis by lysine analogues in lysine-deprived Ehrlich ascites tumour cells. 642 27

Normal volunteers were evaluated in the postabsorptive state, following 10 days of protein-calorie starvation, and during intravenous feeding ( ivf ) to determine the impact of nutritional status upon exertion-induced muscle amino acid metabolism. An isolated forearm model allowed an evaluation of recovery of metabolism following 1 min of submaximal isotonic exercise. Forearm blood flow returned to near basal levels within 15 min after exertion during postabsorptive and ivf conditions, but remained greater than or equal to 150% of basal at 1 hr after exercise during starvation. At 30 and 60 min after exercise, forearm plasma flux of total and essential amino acids were unchanged from basal in the postabsorptive state. However, the pattern of essential amino acid flux demonstrated a relative reduction in isoleucine and leucine efflux compared with basal, and this pattern persisted throughout 1 hr of recovery. During starvation, a significant (P less than 0.05) increase in total and essential amino acid efflux was observed throughout the recovery period. Starvation was also associated with significant increases in alanine and lysine efflux during recovery. Intravenous feeding was associated with a significant (P less than 0.05) uptake of essential amino acids with respect to basal levels at 30 min after exercise. At 60 min, there was a shift to total amino acid efflux but no change from basal flux for essential amino acids. During ivf , the pattern of essential amino acid uptake returned to basal within 1 hr after exertion.
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PMID:Influence of nutritional status on exertion-induced forearm amino acid metabolism in normal man. 642 22


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