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

The beta chain of rabbit (Oryctolagus caniculus) hemoglobin has previously been reported to contain a single residue of isoleucine at beta(112). We have detected other rabbits with either zero isoleucyl residues or half a residue per beta chain. This character is polymorphic and inherited as a simple mendelian autosomal codominant.-Normally the modal number of ribosomes per polyribosome is 4 to 6 in reticulocyte lysates; but incubation of rabbit reticulocytes prior to lysis with L-o-methylthreonine (OMT), an isostere of isoleucine, leads to a bimodal distribution in lysates with 2-3 and 8-12 ribosomes as modes. This alteration has been attributed to ribosomal traffic jams caused by starvation for ile-tRNA at mRNA codons corresponding to the locations of isoleucyl residues at positions alpha(10), alpha(17), alpha(55) and beta(112). We have confirmed this interpretation by incubating OMT with reticulocytes from rabbits with integral, half integral and nil values for isoleucyl residues per beta chain to show that formation of the larger clusters of polyribosomes requires that beta(112) = ile.
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PMID:An electrophoretically silent polymorphism for the beta chains of rabbit hemoglobin and associated polyribosome patterns. 481 67

1. At 3 min after an intravenous injection of radioactive amino acids into the rat, the bulk of radioactivity associated with liver polyribosomes can be interpreted as growing peptides. 2. In an attempt to identify the rate-limiting step of protein synthesis in vivo and in vitro, use was made of the action of puromycin at 0 degrees C, in releasing growing peptides only from the donor site, to study the distribution of growing peptides between the donor and acceptor sites. 3. Evidence is presented that all growing peptides in a population of liver polyribosomes labelled in vivo are similarly distributed between the donor and acceptor sites, and that the proportion released by puromycin is not an artifact of methodology. 4. The proportion released by puromycin is about 50% for both liver and muscle polyribosomes labelled in vivo, suggesting that neither the availability nor binding of aminoacyl-tRNA nor peptide bond synthesis nor translocation can limit the rate of protein synthesis in vivo. Attempts to alter this by starvation, hypophysectomy, growth hormone, alloxan, insulin and partial hepatectomy were unsuccessful. 5. Growing peptides on liver polyribosomes labelled in a cell-free system in vitro or by incubating hemidiaphragms in vitro were largely in the donor site, suggesting that either the availability or binding of aminoacyl-tRNA, or peptide bond synthesis, must be rate limiting in vitro and that the rate-limiting step differs from that in vivo. 6. Neither in vivo nor in the hemidiaphragm system in vitro was a correlation found between the proportion of growing peptides in the donor site and changes in the rate of incorporation of radioactivity into protein. This could indicate that the intracellular concentration of amino acids or aminoacyl-tRNA limits the rate of protein synthesis and that the increased incorporation results from a rise to a higher but still suboptimum concentration.
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PMID:The rate-limiting step of protein synthesis in vivo and in vitro and the distribution of growing peptides between the puromycin-labile and puromycin-non-labile sites on polyribosomes. 511

To determine the stringent response, a repression of gene activity during amino acid starvation assumed to be mediated by the effector necleotide guanosine tetraphosphate (ppGpp), of metabolically regulated constitutive genes, we measured the transcription of ribosomal protein genes, the constitutive lac operon, and stable RNA genes in a variety of growth media and after amino acid starvation in a relA+/relA pair of Escherichia coli B/r strains. For rRNA and tRNA (stable RNA) it has previously been shown that the distinction between stringent control and growth rate control is unfounded, as the function describing the stable RNA gene activities at different concentrations of guanosine tetraphosphate is independent of growth conditions (exponential growth or amino acid starvation) and of the relA allele present. Here, the results indicated that the stringent responses of ribosomal protein genes and lac differ from their metabolic control during exponential growth in different media. This can be explained by polarity and RNA polymerase sink effects during amino acid starvation which are irrelevant for stable RNA genes but which are superimposed on mRNA gene activities.
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PMID:Transcription of ribosomal component genes and lac in a relA+/relA pair of Escherichia coli strains. 609 Mar 95

Amount of guanosine-5'-triphosphate, 3'-diphosphate (pppGpp) and guanosine-5'-diphosphate, 3'-diphosphate (ppGpp) in the cells of b. subtilis increased several times during starvation for lysine or after treatment with serine hydroxamate (analog of serine) or norvaline (analog of leucine), or in the presence of trimethoprim, which induced deficiency of methionine and leucine. In exponentially growing cells the concentration of pppGpp was found to be 10-20 pmol/A600. When serine hydroxamate or trimethoprim were added, concentration of pppGpp increased to 500-800 pmol/A600 and then slowly diminished. Elimination of lysine or addition to the culture medium of norvaline caused slight transitory accumulation of pppGpp (150 pmol/A600). The amount of another nucleotide ppGpp was always 2-3 times lower than one of pppGpp. Accumulation of (p)ppGpp in rel+ cells was accompanied by cessation of stable RNA synthesis. Under conditions described above rel- cells continued RNA synthesis and did not accumulate (p)ppGpp. In the rel+ cells treated with serine hydroxamate synthesis of stable RNA resumed and the amount of (p)ppGpp decreased after addition of serine or tetracycline and chloramphenicol. The half-life period for pppGpp in the presence of chloramphenicol was determined to be 30-40 seconds. Thus, during aminoacyl-tRNA deficiency rel+ cells of B. subtilis accumulate (p)ppGpp, which are believed to participate in negative regulation of RNA synthesis. Slight accumulation of pppGpp without concomitant inhibition of stable RNA synthesis was observed after treatment of growing cells with chloramphenicol.
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PMID:[Guanosine polyphosphate concentration and stable RNA synthesis in Bacillus subtilis following suppression of protein synthesis]. 616 Mar 84

The response of the thermophile Bacillus stearothermophilus to inhibition of tRNA acylation, energy starvation and temperature downshift was characterized. We found that B. stearothermophilus, like other prokaryotic organisms, reacts with the so-called stringent response, which includes the accumulation of the unusual nucleotides guanosine 3',5' bis (diphosphate) [ppGpp] and guanosine 3'-diphosphate, 5'-tri-phosphate [pppGpp] and concomitantly the reduction of RNA synthesis and growth rate. The amount of (p)ppGpp formed depended on the cause of the stringent response: when tRNA acylation was inhibited (p)ppGpp synthesis was much higher than after energy starvation or temperature downshift whereas RNA synthesis was totally blocked in each case.
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PMID:The stringent response to unacylated tRNA, energy-and temperature-downshift in Bacillus stearothermophilus. 616 48

Parameters relating to RNA synthesis were measured after a temperature shift from 30 to 42 degrees C, in a relA+ and relA- isogenic pair of Escherichia coli strains containing a temperature-sensitive valyl tRNA synthetase. The following results were obtained: (i) the rRNA chain growth rate increased 2-fold in both strains; (ii) newly synthesized rRNA became unstable in both strains; (iii) the stable RNA gene activity (rRNA and tRNA, measured as stable RNA synthesis rate relative to the total instantaneous rate of RNA synthesis) decreased 1.7-fold in the relA+ strain and increased 1.9-fold in the relA mutant; and (iv) the RNA polymerase activity (measured by the percentage of total RNA polymerase enzyme active in transcription an any instant) decreased from 20 to 3.6% in the relA+ strain and remained unchanged (or increased at most to 22%) in the relA mutant. It is suggested that both rRNA gene activity and the RNA polymerase activity depend on the intracellular concentration of guanosine tetraphosphate, whereas the altered chain elongation rate and stability of rRNA are temperature or amino acid starvation effects, respectively, without involvement of relA function.
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PMID:relA-dependent RNA polymerase activity in Escherichia coli. 617 1

The expression of stable RNA (rRNA and tRNA) genes and the concentration of guanosine tetraphosphate (ppGpp) were measured in an isogenic pair of relA+ and relA derivatives of Escherichia coli B/r. The cells were either growing exponentially at different rates or subject to amino acid starvation when they were measured. The specific stable RNA gene activity (rs/rt, the rate of rRNA and tRNA synthesis relative to the total instantaneous rate of RNA synthesis) was found to decrease from 1.0 at a ppGpp concentration of 0 (extrapolated value) to 0.24 at saturating concentrations of ppGpp (above 100 pmoles per optical density at 460 nm unit of cell mass). The same relationship between the rs/rt ratio and ppGpp concentration was obtained independent of the physiological state of the bacteria (i.e., independent of the growth rate or of amino acid starvation) and independent of the relA allele. It can be concluded that ppGpp is an effector for stable RNA gene control and that stable RNA genes are not controlled by factors other than the ppGpp-mediated system. The results were shown to be qualitatively and quantitatively consistent with data on in vitro rRNA gene control by ppGpp, and they were interpreted in the light of reported ideas derived from those in vitro experiments.
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PMID:Control of rRNA and tRNA syntheses in Escherichia coli by guanosine tetraphosphate. 617 24

Methods have been developed to analyze the kinetics of digestion of chromatin by nucleases. Radioactively labeled nuclei were incubated with enzyme in an ultrafiltration apparatus and digestion rates of different chromatin samples were computed employing a least-squares curve fitting technique to fit the data to zero-order and/or first-order kinetic models. These methods allow detailed kinetic analyses on small amounts of chromatin. Two biological systems were studied. 1) Tetrahymena thermophila macronuclei and micronuclei were compared; these nuclei differ in their transcriptional activities. 2) Ribosomal DNA (rDNA) of Tetrahymena pyriformis, approximately 60% of which codes for rRNA, can be preferentially labeled during starvation-refeeding; its digestion kinetics relative to bulk chromatin were studied. DNase I digested 20-40% of the macromolecular DNA about 3 times faster than bulk macronuclear or micronuclear DNA, and 60-80% of ribosomal gene-containing chromatin about 5 times faster than bulk chromatin. Filter hybridization studies of the DNAase I sensitivity of tRNA, 5S RNA, and ribosomal genes yielded similar results. These data are consistent with the observation that transcribed genes are especially sensitive to attach by DNase I and suggest that activated chromatin structure as probed by extensive DNase I digestion is the same in higher and lower eucaryotes for genes transcribed by all three RNA polymerases. Digestion kinetics of micrococcal nuclease were found to depend on the digestion conditions employed. These two biological systems and the methods we have developed should facilitate analyses of the factors responsible for maintaining an active chromatin structure.
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PMID:Nuclease sensitivity of chromatin containing active genes: kinetic analyses utilizing continuous elution of digestion products from an ultrafiltration cell. 627 9

In yeast, as in other organisms, amino acid biosynthetic pathways share a common regulatory control. The manifestation of this control is that derepression of the enzymes belonging to several amino acid biosynthetic pathways follows amino acid starvation or tRNA discharging. The arginine anabolic and catabolic pathways are, in addition, regulated specifically by arginine in opposite ways by common regulators. We have measured the mRNA levels for four genes subject to the general amino acid control: HIS4, ARG3, ARG4 and CPAII and compared them to the corresponding enzyme levels. Similarly we have measured the mRNA levels for two genes subject to the arginine specific regulation: ARG3 and CAR1, the former gene belongs to the arginine anabolic pathway and the latter to the arginine catabolic one. HIS4, ARG4 and CPAII enzyme and messenger amounts are perfectly coordinated in all the conditions of general repression or derepression tested. However, arginine does not reduce the level of the ARG3 mRNA enough to explain the reduction of ornithine carbamoyltransferase activity nor does it increase the level of the CAR1 mRNA enough to explain the extent of induction of arginase. Coordination of enzyme and ARG3 mRNA is achieved only when the specific control is eliminated. The half-lives of the ARG3 and CAR1 messengers are enhanced in mutants leading to constitutive expression of ornithine carbamoyltransferase and arginase. These data suggest that the control that coordinates the synthesis of all the amino acids in the yeast cell operates at the level of transcription while the arginine specific regulatory mechanism seems to operate at a post-transcriptional level.
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PMID:Participation of transcriptional and post-transcriptional regulatory mechanisms in the control of arginine metabolism in yeast. 634 80

The involvement of undermodified tRNA in the regulation of the ilvGEDA operon has been investigated using Escherichia coli C6, a relA-, Cys-, Met- mutant. This strain accumulates thionucleotide-deficient or methyl-deficient tRNA when starved for cysteine or methionine, respectively. The levels of threonine deaminase, the ilvA gene product, and transaminase B, the ilvE gene product, were both lower in cysteine-starved cells, as compared with either growing or methionine-starved cultures. When cysteine was added to cysteine-starved cells, growth ensued promptly and both enzyme activities returned to control levels. Treatment of recovering cultures with valine limited growth by isoleucine limitation, but did not cause a derepression of the ilvGEDA operon. Valine treatment of nonstarved or methionine-starved cells led to the expected increase in threonine deaminase and transaminase B activities. Cysteine-starved cells slowly regained the ability to derepress the operon after 3 h of recovery in complete medium. In contrast, the induction of the lac operon was normal in cysteine-starved cultures, even in the presence of valine. The loss of derepressibility of the ilvGEDA operon was correlated with the presence of a kinetically and chromatographically altered tRNAIle in cysteine-starved cells. No changes in tRNAIle were observed after methionine starvation. Using the periodate method, we found that the charging of tRNAIle increased from the normal level of 60 to 80% or greater after starvation for cysteine. Under conditions where the ilvGEDA operon was fully derepressed in nonstarved cells, the charging of tRNAIle fell to 27%. Unexpectedly, nearly identical results were obtained with cysteine-starved cells after an identical derepression test. These results suggest that factors other than the aminoacylation state of tRNAIle may be important in the regulation of this operon. In particular, modifications to tRNA which involve cysteine may be necessary for controlling the expression of the ilvGEDA operon in E. coli.
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PMID:Cysteine starvation, isoleucyl-tRNAIle, and the regulation of the ilvGEDA operon of Escherichia coli. 634 28


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