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

The regulation of uracil uptake in bacteria was studied in bacteriophage T4-infected cells, where host-specific, stable RNA synthesis is completely shut-off by phage, and where phage-specific RNA synthesis, which is not stringently regulated, could be followed by a continuous incorporation of uracil. This incorporation into phage RNA was found to be dependent on the allelic state of the rel gene and it was thus severely restricted under stringent conditions. This was not the case with adenine, which was incorported into RNA to almost the same extent under stringent and relaxed conditions, respectively. The inhibition of uracil uptake under proceeding RNA formation, which was furthermore found to be reversed by addition of chloramphenicol, indicated a specific mechanism governing the cellular entry of uracil. This is suggested to involve the allosteric regulation of uracil phosphoribosyltransferase (EC 2.4.2.9.). The enzyme was partially purified by ammonium sulfate precipitation and gel chromatography. The dependence on GDP and GTP as positive effectors was demonstrated. The stimulatory effect of GTP was abolished in vitro by the addition of guanosine 5'-diphosphate 3-diphosphate, which is known to accumulate during amino acid starvation in stringent bacteria. The reversible inactivation of the enzyme by dilution suggested a subunit structure of uracil phosphoribosyltransferase.
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PMID:Biochemical mechanism of uracil uptake regulation in Escherichia coli B. Allosteric effects on uracil phosphoribosyltransferase under stringent conditions. 33 63

A thermosensitive conditional yeast mutant (ts-187) which suppresses protein synthesis at the nonpermissive temperature (36 degrees C) also suppresses RNA synthesis. The effect of temperature on the mutant is similar to the addition of cycloheximide--it inhibits the incorporation of labeled precursors into RNA in both whole cells and isolated nuclei. The effect of temperature is selective for the RNA polymerases bound to the nuclear template but not for the total RNA polymerases. Thus, the specific activities and total amounts of RNA polymerase species extracted and assayed with exogenous DNA template are similar in the ts-187 cultured at 23 degrees C and at 36 degrees C. On the contrary, the nuclear polymerases, i.e., RNA synthesis in isolated nuclei, are dramatically inhibited in cells cultured at 36 degrees C. When amino acid starved ts-187 cells are transferred to 36 degrees C, release from the inhibtion of RNA synthesis is observed. As with the addition of cycloheximide, this relaxation is observed in cells but not in isolated nuclei. The parental strain, A364A, which responds by stimulating instead of inhibiting protein synthesis when the temperature is increased to 36 degrees C, also exhibits an inhibition in the incorporation of labeled precursor into RNA as well as reducing RNA synthesis in isolated nuclei. However, these are transitory inhibitions and afterward there is reinitiation of both processes. Reinitiation of RNA synthesis in isolated nuclei is similar to the relaxed phenomenon and it is called "nuclear relaxation". This relaxation can only be obtained if protein synthesis is not inhibited; however, cellular relaxation occurs in the absence of protein synthesis. The repression of the nuclear RNA polymerase activities which starvation and inhibition of protein synthesis produce appears to be due to a restriction in the nuclear DNA template. This notion is supported by the fact that a net diminution of these nuclear enzyme activities is observed in spheroplasts cultured under starving conditions. Studies of the four main ribonucleotide pools indicate that stringency and inhibition of protein synthesis (ts-187 cultured at 36 degrees C) produce an increase in UTP and CTP pools. This is consistent with the concept that stringency and inhibition of protein synthesis affect the rate of utilization rather than the synthesis of these ribonucleotide residues. In the A364A and ts-187 yeast strains, the conversion of uracil but not of uridine into the UTP and CTP is inhibited when there is inhibition of the nuclear RNA polymerases. This indicates that the uracil phosphoribosyltransferase but not the uridine-cytidine kinase is allosterically inhibited by UTP and CTP in yeast. The feedback inhibition in the metabolic pathway of the base explains why relaxation cannot be detected when uracil instead of uridine is used as the labeled RNA precursor.
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PMID:Control of ribonucleic acid synthesis in eukaryotes. 2. The effect of protein synthesis on the activities of nuclear and total DNA-dependent RNA polymerase in yeast. 77 13

The upp gene coding for uracil phosphoribosyltransferase was subcloned on a 5-kb EcoRI restriction fragment along with the purMN operon. By a combination of complementation, deletion and minicell analyses, the upp gene was located adjacent to and divergently transcribed from the purMN operon. All three gene products could be identified in minicell extracts. The cloned upp gene shows an elevated expression upon uracil starvation. The nucleotide sequence and transcription start of the gene were determined. The sequence yields an open reading frame of 624 nucleotides encoding a protein of 22.5 kDa which is in agreement with the previously determined subunit Mr of the purified enzyme. A putative 5-phosphoribosyl-alpha-1-diphosphate (PRPP) binding site has been identified which is similar to the PRPP binding site of the yeast uracil phosphoribosyltransferase.
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PMID:Characterization of the upp gene encoding uracil phosphoribosyltransferase of Escherichia coli K12. 137 Dec 55

Uracil phosphoribosyltransferase from Escherichia coli K12 was purified to homogeneity as determined by polyacrylamide gel electrophoresis. For this purpose a pyrimidine-requiring strain harboring the upp gene on a ColE1 plasmid was used, which showed 15-times higher uracil phosphoribosyltransferase activity in a crude extract. When this strain was grown under conditions of uracil starvation, an additional 10-times elevation of the enzyme activity was obtained. The molecular weight of uracil phosphoribosyltransferase was determined to be 75000; the enzyme consists of three subunits with a molecular weight of 23500. Uracil phosphoribosyltransferase is specific for uracil and some uracil analogues. The apparent Km values for uracil and PRib-PP were 7 microM and 300 microM, respectively. As an effector of enzyme activity, GTP lowered the Km for PRib-PP to 90 microM and increased the Vmax value 2-fold, but had no effect on the Km for uracil. The effect of GTP was found to be pH-dependent. The enzymatic characterization of uracil phosphoribosyltransferase and the observed regulation of its synthesis emphasizes the role of the enzyme in pyrimidine salvage.
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PMID:Purification and some properties of uracil phosphoribosyltransferase from Escherichia coli K12. 351 46

Arabidopsis seedlings grown for 14 d without phosphate (P) exhibited stunted growth and other visible symptoms associated with P deficiency. RNA contents in shoots decreased nearly 90%, relative to controls. In shoots, expression of Pht1;2, encoding an inducible high-affinity phosphate transporter, increased threefold, compared with controls, and served as a molecular marker for P limitation. Transcript levels for five enzymes (aspartate transcarbamoylase, ATCase, EC 2.1.3.2; carbamoyl phosphate synthetase, CPSase, EC 6.3.5.5); UMP synthase, EC 2.4.1.10, EC 4.1.1.23; uracil phosphoribosyltransferase, UPRTase, EC 2.4.2.9; UMP kinase, EC 2.7.1.14) increased 2-10-fold in response to P starvation in shoots. These enzymes, which utilize phosphorylated intermediates at putative regulated steps in de novo synthesis and salvaging pathways leading to UMP and pyrimidine nucleotide formation, appear to be coordinately regulated, at the level of gene expression. This response may facilitate pyrimidine nucleotide synthesis under P limitation in this plant. Expression of P-dependent and P-independent phosphoribosyl pyrophosphate (PRPP) synthases (PRS2 and PRS3, respectively) which provide PRPP, the phosphoribosyl donor in UMP synthesis via both de novo and salvaging pathways, was differentially regulated in response to P limitation. PRS2 mRNA levels increased twofold in roots and shoots of P-starved plants, while PRS3 was constitutively-expressed. PRS3 may play a novel role in providing PRPP to cellular metabolism under low P availability.
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PMID:Effects of phosphate limitation on expression of genes involved in pyrimidine synthesis and salvaging in Arabidopsis. 1582 Jun 55