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

The acid-soluble ribonucleic acid degradation products formed by Escherichia coli cells starved for a carbon source have been identified. They comprise oligonucleotides, nucleoside diphosphates, 5'- and 3'-nucleoside monophosphates, nucleosides, and free bases. The majority of these products are excreted phates, nucleosides, and free bases. The majority of these products are excreted into the medium, and only small and constant amounts are kept in the pool. During carbon starvation at elevated temperatures, mutants deficient in ribonuclease I do not form oligonucleotides and 3'-nucleoside monophosphates, and mutants that contain a modified form of polynucleotide phosphorylase do not accumulate nucleoside diphosphates. 5'-Nucleoside monophosphates do accumulate, however, in a mutant containing thermoabile ribonuclease II, under conditions where more than 95% of all enzyme activity had been destroyed. The data presented confirm the participation of ribonuclease I and polynucleotide phosphorylase in the final steps of ribonucleic acid degradation and indicate that an exonuclease forming 5'-nucleoside monophosphates is also involved.
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PMID:Accumulation of nucleotides by starved Escherichia coli cells as a probe for the involvement of ribonucleases in ribonucleic acid degradation. 32 Jan 88

The disappearance of ribosomes in Escherichia coli cells starved for a carbon source was studied. We used a series of mutants, some of them lacking in ribonuclease I(RNase I, EC 2.7.7.17), and other containing various combinations of modified polynucleotide phosphorylase (PNPase, EC 2.7.7.8) and modified ribonuclease II (RNase II, EC 3.1.4.1). RNA was prepared from the starved mutant cells and separated on polyacrylamide gels. The results obtained indicate that 23 S RNA degradation is similar in all strains that lack RNase I, and is slightly increased in the strain that contains this enzyme. The extent of 16 S RNA degradation is identical in all strains tested. RNA species in the size of 4 S and smaller accumulate in mutants containing modified forms of PNPase and RNase II. The appearance of an RNA species 10% smaller than 16 S RNA (d16 S RNA) was observed in all strains that contain unmodified RNase II. Analysis of ribosomes and polysomes and their RNA content indicated that polysomes are converted to monosomes and these, in turn, to ribosomal subunits. No RNA degradation products were found in polysomes, 70 S, OR 50 C particle; 30 S subunits contained 16 S RNA as well as the d16 S RNA species. Subunits are degraded to a similar extent in all strains lacking RNase I, and at a slightly faster rate in the strain that contains RNase I. The RNA to protein ratio in subunits prepared from starved cells is similar to that of unstarved cultures. Very little degradation of ribosomal proteins occurs in these mutants during carbon starvation. The proteins released from degraded ribosomes are found in the fast sedimenting (20,000 times g) pellet. Cell viability studies indicated a direct correlation between the capacity of the mutants to recovery from starvation and their capacity to degrade RNA. Thus a biological necessity for degradation of ribosomes during starvation is implied. Based on these data we propose that the endonucleolytic degradation of ribosomal RNA is the primary event in starvation degradation. It takes place in ribosomal subunits, which fall apart after the endonucleoltic attack. The RNA pieces produced by this cleavage are degraded to nucleotide by RNase II and PNPase. The ribosomal proteins attach to the cell membrane.
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PMID:The fate of ribosomes in Escherichia coli cells starved for a carbon source. 108 66

Decay of pre-existing ribonucleic acid was studied in Escherichia coli cells subjected to high temperature or to starvation for nitrogen, phosphate, amino acids, or a carbon source. In these studies a series of mutants affected in ribonucleic I(RNase I, EC 3.1.4.22) polynucleotide phosphorylase (EC 2.7.7.8) or ribonuclease II (RNase II, EC 3.1.4.23) were used. Degradation of total RNA and the disappearance of 23 S and 16 S rRNA were followed. The results obtained indicated that, by and large, decay of 23 S and 16 S RNA parallels that of total RNA. Decay of RNA depended on the nuclease content of the cells as well as on the treatment of applied. It was most pronounced during carbon starvation and least in cells deprived of phosphate ions. It was most effective in strains containing all three nucleases and least in the strain defective in all three. The exonucleases polynucleotide phosphorylase and RNase II did not seem to affect the extent of 23 S and 16 S RNA disappearance. Strains with modified exonucleases did accumulate low molecular weight RNA species during treatments which induced considerable degradation of 23 S and 16 S RNA. Based on the above date and previous observations, we suggest that during various starvations a similar mechanism is operative. The 23 S and 16 S RNAs are degraded endonucleolytically, and this is the rate-limiting step during starvation. The exonucleases polynucleotide phosphorylase and RNase II seem to participate primarily in the decay of the low molecular weight RNA species formed by the endonuclease(s), not as yet identified.
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PMID:Decay of ribosomal ribonucleic acid in Escherichia coli cells starved for various nutrients. 109 48

The suggested involvement of ribonuclease II in the maturation of rRNA has been examined directly by determining the activity of the enzyme and the amount of p16S rRNA in cell-free extracts from Escherichia coli A19 and its temperature-sensitive derivative N464 grown under experimental conditions designed to vary the amounts of enzyme and precursor independently. In strain A19 the enzyme showed maximum activity in circumstances where the amount of p16S rRNA was normal (e.g. exponential-phase cells) or raised eight times (e.g. during inhibition of growth by methionine starvation of the relaxed auxotroph or by chloramphenicol or puromycin treatment). In strain N464 at the non-permissive temperature the ribonuclease II activity may be decreased by 50% without effect upon the amount of p16S rRNA, whereas in methionine starvation of this strain the enzyme activity is at a maximum and the p16S rRNA is eight times that in exponential-phase cells. These observations are discussed in relation to the previously implied role of ribonuclease II in the maturation of rRNA within ribosome precursors.
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PMID:The role of ribonuclease II in the maturation of precursor 16S ribosomal ribonucleic acid in Escherichia coli. 461 96

A mutant strain of Escherichia coli that fails to recover from prolonged (72 hr) starvation also fails to grow at 43 C. Extracts of this mutant strain show an increased ribonuclease II activity as compared to extracts of the parental strain, and stable ribonucleic acid is degraded to a larger extent in this strain during starvation. Ts(+) transductants and revertants were tested for all the above-mentioned phenotypes. All the Ts(+) transductants and revertants tested behaved like the Ts(+) parental strain, which suggests that all the observed phenotypes are caused by a single sts (starvation-temperature sensitivity) mutation. The reversion rate from sts(-) to sts(+) is rather low but is within the range of reversion rates for other single-site mutations. Three-point transduction crosses located this sts mutation between the ilv and rbs genes. The properties of sts(+)/sts(-) merozygotes suggested that the Ts(-) phenotype of this mutation is recessive.
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PMID:Genetic analysis of an Escherichia coli syndrome. 494 97

A multiple mutant strain of Escherichia coli containing mutations affecting the exoribonucleases, RNase II, RNase D, and RNase BN, and also the endonuclease, RNase I, was constructed by P1-mediated transduction. Extracts of the mutant strain were lacking the aforementioned RNase activities. The multiple mutant displayed normal growth in both rich and minimal media at a variety of temperatures, recovered from starvation essentially as the wild-type parent, and could support the growth of a variety of bacteriophages. In addition, RNA synthesis was normal and no precursor RNA accumulation was observed. The properties of the mutant strain indicate that the three exoribonucleases are not essential for the viability of E. coli. The implications of these findings to our understanding of RNA processing and degradation are discussed.
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PMID:A multiple mutant of Escherichia coli lacking the exoribonucleases RNase II, RNase D, and RNase BN. 620 70

Cells respond to adverse environmental conditions by synthesizing new proteins or elevating the levels of pre-existing ones that are needed to cope with the particular stress situation. We show here that Escherichia coli RNase R, a processive 3'-to5'-exoribonuclease, is dramatically increased in response to a variety of different stress conditions. Elevation of RNase R activity by as much as 10-fold was observed in response to entry into stationary phase, starvation, and cold shock, and a approximately 3-fold increase was seen during growth in minimal medium compared with rich medium. The elevation in RNase R activity was associated primarily with an increase in RNase R protein. RNase R was previously implicated in quality control of rRNA and tRNA and in the decay of mRNAs with extensive secondary structure. Its dramatic increase under multiple stress conditions suggests extensive remodeling of structured RNA in response to the altered environment.
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PMID:Elevation of RNase R in response to multiple stress conditions. 1613 21

A prominent enzyme in organellar RNA metabolism is the exoribonuclease polynucleotide phosphorylase (PNPase), whose reversible activity is governed by the nucleotide diphosphate-inorganic phosphate ratio. In Chlamydomonas reinhardtii, PNPase regulates chloroplast transcript accumulation in response to phosphorus (P) starvation, and PNPase expression is repressed by the response regulator PSR1 (for PHOSPHORUS STARVATION RESPONSE1) under these conditions. Here, we investigated the role of PNPase in the Arabidopsis (Arabidopsis thaliana) P deprivation response by comparing wild-type and pnp mutant plants with respect to their morphology, metabolite profiles, and transcriptomes. We found that P-deprived pnp mutants develop aborted clusters of lateral roots, which are characterized by decreased auxin responsiveness and cell division, and exhibit cell death at the root tips. Electron microscopy revealed that the collapse of root organelles is enhanced in the pnp mutant under P deprivation and occurred with low frequency under P-replete conditions. Global analyses of metabolites and transcripts were carried out to understand the molecular bases of these altered P deprivation responses. We found that the pnp mutant expresses some elements of the deprivation response even when grown on a full nutrient medium, including altered transcript accumulation, although its total and inorganic P contents are not reduced. The pnp mutation also confers P status-independent responses, including but not limited to stress responses. Taken together, our data support the hypothesis that the activity of the chloroplast PNPase is involved in plant acclimation to P availability and that it may help maintain an appropriate balance of P metabolites even under normal growth conditions.
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PMID:Abnormal physiological and molecular mutant phenotypes link chloroplast polynucleotide phosphorylase to the phosphorus deprivation response in Arabidopsis. 1971 Feb 29

Cellular adaptations to stress often involve changes in RNA metabolism. One RNA-binding protein that has been implicated in RNA handling during environmental stress in both animal cells and prokaryotes is the Ro autoantigen. However, the function of Ro in stress conditions has been unknown. We report that a Ro protein in the radiation-resistant eubacterium Deinococcus radiodurans participates in ribosomal RNA (rRNA) degradation during growth in stationary phase, a form of starvation. Levels of the Ro ortholog Rsr increase dramatically during growth in stationary phase and the presence of Rsr confers a growth advantage. Examination of rRNA profiles reveals that Rsr, the 3' to 5' exoribonuclease polynucleotide phosphorylase (PNP) and additional nucleases are all involved in the extensive rRNA decay that occurs during starvation of this bacterium. We show that Rsr, PNP, and an Rsr-PNP complex exhibit increased sedimentation with ribosomal subunits during stationary phase. As the fractionation of PNP with ribosomal subunits is strongly enhanced in the presence of Rsr, we propose that Ro proteins function as cofactors to increase the association of exonucleases with certain substrates during stress.
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PMID:A role for a bacterial ortholog of the Ro autoantigen in starvation-induced rRNA degradation. 2016 Jan 19

Ribosomal RNAs are generally stable in growing Escherichia coli cells. However, their degradation increases dramatically under conditions that lead to slow cell growth. In addition, incomplete RNA molecules and molecules with defects in processing, folding, or assembly are also eliminated in growing cells in a process termed quality control. Here, we show that there are significant differences between the pathways of ribosomal RNA degradation during glucose starvation and quality control during steady-state growth. In both processes, endonucleolytic cleavage of rRNA in ribosome subunits is an early step, resulting in accumulation of large rRNA fragments when the processive exoribonucleases, RNase II, RNase R, and PNPase are absent. For 23S rRNA, cleavage is in the region of helix 71, but the exact position can differ in the two degradative processes. For 16S rRNA, degradation during starvation begins with shortening of its 3' end in a reaction catalyzed by RNase PH. In the absence of this RNase, there is no 3' end trimming of 16S rRNA and no accumulation of rRNA fragments, and total RNA degradation is greatly reduced. In contrast, the degradation pattern in quality control remains unchanged when RNase PH is absent. During starvation, the exoribonucleases RNase II and RNase R are important for fragment removal, whereas for quality control, RNase R and PNPase are more important. These data highlight the similarities and differences between rRNA degradation during starvation and quality control during steady-state growth and describe a role for RNase PH in the starvation degradative pathway.
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PMID:Degradation of ribosomal RNA during starvation: comparison to quality control during steady-state growth and a role for RNase PH. 2113 37


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