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

The restriction point (R) separates two functionally different parts of G1 in continuously cycling cells. G1-pm represents the postmitotic interval of G1 that lasts from mitosis to R. G1-ps represents the pre S phase interval of G1 that lasts from R to S. G1-pm is remarkably constant in length (its duration is about three hours) in the different cell types studied so far. G1-ps, however, varies considerably, indicating that entry into S is not directly followed after passage through R. Progression through G1-pm requires continuous stimulation by mitogenic signals (e.g. growth factors) and a high rate of protein synthesis. Interruption of the mitogenic signals or moderate inhibition of protein synthesis leads to a rapid exit from the cell cycle to G0 in normal (untransformed) cells. Upon restimulation with mitogenic signals, the cell returns to the same point in G1-pm from which it left the cell cycle. Thus the cell seems to have a memory for how far it has advanced through G1-pm, suggesting that a continuous structural alteration, for example chromatin decondensation, takes place in G1. The molecular background to transition from growth factor dependence in G1-pm to growth factor independence in G1-ps (a switch which represents commitment to a new cell cycle and passage through R) is still not fully understood. Cyclin-dependent kinase (cdk)-mediated hyperphosphorylation of the retinoblastoma protein (Rb), and concomitant liberation (and activation) of members of the E2F family of transcription factors, are probably important aspects of R control in normal cells. A key component here could be cdk2 activity which is controlled by cyclin E. When cdk2 activity starts to increase rapidly in G1, due to activation of a positive feedback loop, it reaches a critical level above which cdk inhibitors (CKIs) such as p21 and p27 are outweighed; the cell has then become independent of mitogenic and inhibitory signals and is committed to a new cell cycle. However, other components are probably also involved in R control. For instance, a 'cryptic' R (a G1-pm-like state) can be induced even in tumour cells that do not respond to growth factor starvation or protein synthesis inhibitors, and are therefore probably defective in the cdk-Rb-E2F pathway. Possibly, a certain degree of chromatin decondensation has to take place after mitosis in order to allow transcription of, for example, the cyclin E gene or other critical E2F targets. Although the molecular basis for restriction point control still remains unclear, we can expect rapid progress in this important field over the next few years.
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PMID:What is the restriction point? 860 14

In growing Escherichia coli K12 cells, the cryptic bgl operon is activated 98% of the time by insertions of IS1 or IS5 into the control region, designated bglR. The activated bgl operon permits utilization of the beta-glucoside sugar arbutin as a sole carbon and energy source. The bgl operon is also activated by late-occurring mutations during prolonged selection on arbutin. The late-occurring mutations that occurred during prolonged carbon starvation in the presence of arbutin were "adaptive mutations" because they were specific to the presence of arbutin, and they did not occur during prolonged starvation in the absence of arbutin. The spectrum of late-arising mutations differed from that of early-arising, growth-dependent mutations in that 20% of the late-arising mutants resulted from mutations at the hns locus. This provides the first direct evidence for adaptive mutagenesis mediated by the insertion of IS elements. Because no special genetic background is required to select Bgl+ mutants, this affords the opportunity to study IS-element-mediated adaptive mutagenesis in a variety of genetic backgrounds, including the backgrounds of natural isolates of E. coli.
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PMID:Activation of the bgl operon by adaptive mutation. 949 99

When 3 x 10(8) bacteria of the Escherichia coli tyrA14(oc) leu308(am) strain WU3610 are plated on glucose salts agar supplemented with leucine only, colonies of slow-growing Tyr+ suppressor mutants begin to appear after about a week and increase in numbers roughly linearly with time thereafter (stationary phase or starvation-associated mutation). From a library constructed from two of these mutants, a clone was obtained that suppressed the tyrosine requirement of WU3610 when present on a multicopy plasmid. The activity was identified to an open reading frame we call tas, the sequence for which has homology with a variety of known genes with aldo-keto reductase activity. The activity of tas complements the prephenate dehydrogenase dysfunction of tyrA14 (the chorismate mutase activity of tyrA possibly being still functional). A strain deleted for tas showed no spontaneous mutation under starvation conditions. Whereas neither tas+ nor tas bacteria showed any increase in viable or total count when plated under conditions of tyrosine starvation at 3 x 10(8) cells per plate, at lower density (approximately 10(7) per plate) tas+ but not tas bacteria showed considerable residual growth. We suggest that the single copy of tas present in WU3610 allows cryptic cell or DNA turnover under conditions of tyrosine starvation and that this is an essential prerequisite for starvation-associated mutation in this system. The target gene for mutation is not tas, although an increase in the expression of this gene, for example, resulting from a suppressor mutation affecting supercoiling, could be responsible for the slow-growing Tyr+ phenotype.
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PMID:Reversion of the tyrosine ochre strain Escherichia coli WU3610 under starvation conditions depends on a new gene tas. 956 Mar 82

The starvation-stress response (SSR) of Salmonella typhimurium includes gene products necessary for starvation avoidance, starvation survival and virulence for this bacterium. Numerous genetic loci induced during carbon-source starvation and required for the long-term-starvation survival of this bacterium have been identified. The SSR not only protects the cell against the adverse effects of long-term starvation but also provides cross-resistance to other environmental stresses, e.g. thermal challenge (55 degrees C) or acid-pH challenge (pH 2.8). One carbon-starvation-inducible lac fusion, designated stiA was previously reported to be a sigma(S)-dependent SSR locus that is phosphate-starvation, nitrogen-starvation and H2O2 inducible, positively regulated by (p)ppGpp in a relA-dependent manner, and negatively regulated by cAMP:cAMP receptor protein complex and OxyR. We have discovered through sequence analysis and subsequent biochemical analysis that the stiA::lac fusion, and a similarly regulated lac fusion designated sti-99, lie at separate sites within the first gene (narZ) of an operon encoding a cryptic nitrate reductase (narZYWV) of unknown physiological function. In this study, it was demonstrated that narZ was negatively regulated by the global regulator Fnr during anaerobiosis. Interestingly, narZ(YWV) was required for carbon-starvation-inducible thermotolerance and acid tolerance. In addition, narZ expression was induced approximately 20-fold intracellularly in Madin-Darby canine kidney epithelial cells and 16-fold in intracellular salts medium, which is believed to mimic the intracellular milieu. Also, a narZ1 knock-out mutation increased the LD50 approximately 10-fold for S. typhimurium SL1344 delivered orally in the mouse virulence model. Thus, the previously believed cryptic and constitutive narZYWV operon is in fact highly regulated by a complex network of environmental-stress signals and global regulatory functions, indicating a central role in the physiology of starved and stressed cells.
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PMID:The rpoS-dependent starvation-stress response locus stiA encodes a nitrate reductase (narZYWV) required for carbon-starvation-inducible thermotolerance and acid tolerance in Salmonella typhimurium. 1058 11

The concept of transposable elements (TEs) as purely selfish elements is being challenged as we have begun to appreciate the extent to which TEs contribute to allelic diversity, genome building, etc. Despite these long-term evolutionary contributions, there are few examples of TEs that make a direct, positive contribution to adaptive fitness. In E. coli cryptic (silent) catabolic operons can be activated by small TEs called insertion sequences (IS elements). Not only do IS elements make a direct contribution to fitness by activating cryptic operons, they do so in a regulated manner, transposing at a higher rate in starving cells than in growing cells. In at least one case, IS elements activate an operon during starvation only if the substrate for that operon is present in the environment. It appears that E. coli has managed to take advantage of IS elements for its own benefit.
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PMID:Transposable elements as activators of cryptic genes in E. coli. 1095 11

The oriJ-based plasmids contain the origin of DNA replication from the cryptic Rac prophage, present in the chromosomes of most Escherichia coli K-12 strains. The organization of the oriJ replication region resembles that of the bacteriophage lambda, although sequence similarity is small. Here we investigated the regulation of replication of the oriJ-based plasmid in E. coli relA(+) and relA(-) hosts during amino acid starvation and limitation, i.e., during the stringent and relaxed responses. We found that, contrary to plasmids derived from phage lambda, replication of the oriJ-based plasmid proceeds efficiently during both stringent and relaxed responses. On the other hand, density shift experiments and measurement of the stability of a putative replication initiator protein (the lambda O protein homologue) suggest that this replication may be carried out by the heritable replication complex, as previously demonstrated for lambda plasmids. We demonstrate that contrary to bacteriophage lambda p(R) promoter, an analogous promoter from the oriJ region is activated rather than inhibited at increased ppGpp levels. We propose that various responses of these promoters (p(R) and p(R-Rac), which are necessary for transcriptional activation of orilambda and perhaps oriJ, respectively) to ppGpp are responsible for differences in the replication regulation between orilambda- and oriJ-based plasmids during the stringent response.
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PMID:Replication of oriJ-based plasmid DNA during the stringent and relaxed responses of Escherichia coli. 1096 22

Antimutator alleles indentify genes whose normal products are involved in spontaneous mutagenesis pathways. Mutant alleles of the recA and umuC genes of Escherichia coli, whose wild-type alleles are components of the inducible SOS response, were shown to cause a decrease in the level of spontaneous mutagenesis. Using a series of chromosomal mutant trp alleles, which detect point mutations, as a reversion assay, it was shown that the reduction in mutagenesis is limited to base-pair substitutions. Within the limited number of sites than could be examined, transversions at AT sites were the favored substitutions. Frameshift mutagenesis was slightly enhanced by a mutant recA allele and unchanged by a mutant umuC allele. The wild-type recA and umuC genes are involved in the same mutagenic base-pair substitution pathway, designated "SOS-dependent spontaneous mutagenesis" (SDSM), since a recAumuC strain showed the same degree and specificity of antimutator activity as either single mutant strain. The SDSM pathway is active only in the presence of oxygen, since wild-type, recA, and umuC strains all show the same levels of reduced spontaneous mutagenesis anaerobically. The SDSM pathway can function in starving/stationary cells and may, or may not, be operative in actively dividing cultures. We suggest that, in wild-type cells, SDSM results from basal levels of SOS activity during DNA synthesis. Mutations may result from synthesis past cryptic DNA lesions (targeted mutagenesis) and/or from mispairings during synthesis with a normal DNA template (untargeted mutagenesis). Since it occurs in chromosomal genes of wild-type cells, SDSM may be biologically significant for isolates of natural enteric bacterial populations where extended starvation is often a common mode of existence.
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PMID:An aerobic recA-, umuC-dependent pathway of spontaneous base-pair substitution mutagenesis in Escherichia coli. 1116 40

The recently identified role of LeuO in the regulation of transcription has prompted us to search for the specific function(s) of LeuO in bacterial physiology. The cryptic nature of expression of leuO has previously limited such analysis. A conditional leuO expression was found when bacteria enter stationary phase and was shown to be guanosine 3',5'-bispyrophosphate-dependent. Multiple physiological events, including the stringent response, are induced upon the increase of the bacterial stress signal, guanosine 3',5'-bispyrophosphate. In this study, we tested whether LeuO was directly involved in the bacterial stringent response. LeuO was shown to be indispensable for growth resumption following a 2-h growth arrest caused by starvation for branched-chain amino acids in an E. coli K-12 relA1 strain. This result supports a functional role for LeuO in the bacterial stringent response.
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PMID:LeuO expression in response to starvation for branched-chain amino acids. 1137 8

A comprehensive view of the physiological state of Escherichia coli cells at the completion of fermentation processes for biopharmaceutical production was attained via two-dimensional gel electrophoretic analysis of cellular proteins. For high cell density fermentations in which phosphate is depleted to induce recombinant protein expression from the alkaline phosphatase promoter, proteome analysis confirms that phosphate limitation occurs. Known phosphate starvation inducible proteins are observed at high levels; these include the periplasmic phosphate binding protein and the periplasmic phosphonate binding protein. The phn (EcoK) locus of these E. coli K-12 strains remains cryptic, as demonstrated by failure to grow with phosphonate as the sole phosphorus source. Proteome analysis also provided evidence that cells utilize alternative carbon and energy sources during these fermentation processes. To address regulatory issues in the biopharmaceutical industry, comparative electrophoretic analyses were conducted on a qualitative basis for four different fermentation processes. Using this approach, the protein profiles for these processes were found to be highly similar, with the vast majority (85-90%) of proteins detected in all profiles. The observed similarity in proteomes suggests that multiproduct host cell protein immunoassays are a feasible means of quantifying host-derived polypeptides from a variety of biopharmaceutical fermentation processes.
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PMID:Similarity of the Escherichia coli proteome upon completion of different biopharmaceutical fermentation processes. 1199 May 8

The behavior of Aeromonas hydrophila stored at 4 degrees C and 25 degrees C in nutrient-poor filtered sterilized distilled water was investigated. At 4 degrees C, the A. hydrophila population declined below the detection level (0.1 cell mL(-1)) after 7 weeks, whereas the number of cells with intact membrane as determined by the LIVE/DEAD method decreased only by 1 log unit. Although, this response is reminiscent of the so-called VBNC state, the cells could not be resuscitated by an upshift to 25 degrees C. A mixture of rods with normal size and elongated cells was observed in this state. At 25 degrees C, viable cells and cells with intact membrane declined only by 0.8 log unit over the 10-week storage period, and thus A. hydrophila entered the classical starvation survival state. During this state, a mixture of rods and cocci was observed. Prestarvation at 25 degrees C for 24 h and especially 49 days delayed significantly the rate of entry into the VBNC state. However, stationary phase cells were not significantly more tolerant than exponential phase cells. No significant improvements in recovery yield were obtained on LB agar plates amended with catalase or sodium pyruvate. During cold incubation, high variability in responses was observed. Intermittent cryptic regrowth might be responsible for this variability in responses.
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PMID:Starvation survival and viable but nonculturable states in Aeromonas hydrophila. 1202 32


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