Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Washed cells of Salmonella enteritidis harvested from a defined medium during logarithmic growth were subjected to starvation in pH 7 phosphate buffer at 37 C. Viability was measured by slide cultures and plate counts. The survival of cell suspensions equivalent to 1 to 10 mg (dry wt)/ml was influenced by cryptic growth. The rate of cryptic growth, assessed by plate counts, increased with cell density and could not be alleviated by starvation with dialysis. Dialysis of the starving culture did retard the onset of cryptic growth but did not eliminate it, indicating that the major substrates for regrowth were relatively large cellular components. In phosphate buffer, 6.7 homologous heat-killed cells allowed for the doubling of one S. enteritidis cell. Cryptic growth was not observed when cells were starved on the surface of membrane filters or in suspensions equivalent to 20 mug (dry wt)/ml (105 cells/ml). Similar half-life survival times were calculated for both these populations, but the shape of their survival curves differed significantly. These differences were attributed to stress factors encountered during cell preparation and during starvation. The half-life survival time of S. enteritidis starved at 20 mug (dry wt)/ml was 140 h in phosphate buffer, 82 h in 3,6-endomethylene-1,2,3,-6-tetrahydrophthalic acid buffer, and 77 h in tris(hydroxymethyl)aminomethane buffer.
 ...
PMID:Starvation survival of Salmonella enteritidis. 0 69

The Bacillus subtilis tyrS gene, which encodes tyrosyl-tRNA synthetase (TyrTS), was isolated, and its nucleotide sequence was determined. The cloned gene was shown to complement an Escherichia coli tyrS (Ts) mutant. The predicted amino acid sequence exhibited 70% identity to that of Bacillus stearothermophilus TyrTS and 55% identity to that of E. coli TyrTS, while identity to a second cryptic B. subtilis TyrTS gene, designated tyrZ, was only 27%. Primer extension analysis indicated that tyrS transcription initiated at a vegetative promoter sequence located 300 nucleotides upstream of the AUG start codon. The mRNA leader region was found to contain an inverted repeat sequence resembling a transcriptional terminator. Expression of a transcriptional tyrS-lacZ fusion was found to be induced by starvation for tyrosine in a tyrosine auxotroph (tyrA1). Transcription initiation was unaffected by tyrosine starvation. Deletion of the terminator region in a tyrS-lacZ fusion resulted in high-level constitutive expression. Immediately preceding the putative terminator was sequence element found to be conserved in the upstream region of a number of Bacillus tRNA synthetase genes as well as in the ilv-leu biosynthetic operon; mutation of this element in tyrS resulted in low-level uninducible expression. The conservation of this sequence element suggests that aminoacyl-tRNA synthetase genes and the ilv-leu operon may be regulated by a common mechanism in Bacillus spp.
 ...
PMID:Analysis of the Bacillus subtilis tyrS gene: conservation of a regulatory sequence in multiple tRNA synthetase genes. 173 21

We cloned the cryptic phn operon of a K-12 strain, phn(EcoK), and analyzed the nucleotide sequence of the phn region (11,672 bp). An mRNA start site upstream of the phnC gene was identified by S1 nuclease mapping. The pho regulon activator PhoB protects a pho box region near the mRNA start in DNase I footprinting and methylation protection experiments. The sequence of the cryptic phn(EcoK) operon was very similar to that of the functional phn operon of an Escherichia coli B strain, phn(EcoB) (C.-M. Chen, Q.-Z. Ye, Z. Zhu, B. L. Wanner, and C. T. Walsh, J. Biol. Chem. 265:4461-4471, 1990). The phnE(EcoK) gene has an 8-bp insertion, absent from the phnE(EcoB) gene, which causes a frameshift mutation. The spontaneous activation of the cryptic phn(EcoK) operon is accompanied by loss of this additional 8-bp insertion. Studies of the structure, regulation, and function of the phn region suggest that the phosphate starvation-inducible phn operon consists of 14 cistrons from phnC to phnP.
 ...
PMID:Molecular analysis of the cryptic and functional phn operons for phosphonate use in Escherichia coli K-12. 184 May 80

The Escherichia coli phn (psiD) locus encodes genes for phosphonate (Pn) utilization, for phn (psiD) mutations abolish the ability to use as a sole P source a Pn with a substituted C-2 or unsubstituted hydrocarbon group such as 2-aminoethylphosphonate (AEPn) or methylphosphonate (MPn), respectively. Even though the E. coli K-12 phosphate starvation-inducible (psi) phn (psiD) gene(s) shows normal phosphate (Pi) control, Pn utilization is cryptic in E. coli K-12, as well as in several members of the E. coli reference (ECOR) collection which are closely related to K-12. For these bacteria, an activating mutation near the phn (psiD) gene is necessary for growth on a Pn as the sole P source. Most E. coli strains, including E. coli B, are naturally Phn+; a few E. coli strains are Phn- and are deleted for phn DNA sequences. The Phn+ phn(EcoB) DNA was molecularly cloned by using the mini-Mu in vivo cloning procedure and complementation of an E. coli K-12 delta phn mutant. The phn(EcoB) DNA hybridized to overlapping lambda clones in the E. coli K-12 gene library (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987) which contain the 93-min region, thus showing that the phn (psiD) locus was itself cloned and verifying our genetic data on its map location. The cryptic phn(EcoK) DNA has an additional 100 base pairs that is absent in the naturally Phn+ phn(EcoB) sequence. However, no gross structural change was detected in independent Phn+ phn(EcoK) mutants that have activating mutations near the phn locus.
 ...
PMID:Mapping and molecular cloning of the phn (psiD) locus for phosphonate utilization in Escherichia coli. 215 95

Recent reports have called into question the widespread belief "that mutations arise continuously and without any consideration for their utility" (in the words of J. Cairns) and have suggested that some mutations (which Cairns called "directed" mutations) may occur as specific responses to environmental challenges, i.e., they may occur more often when advantageous than when neutral. In this paper it is shown that point mutations in the trp operon reverted to trp+ more frequently under conditions of prolonged tryptophan deprivation when the reversions were advantageous, than in the presence of tryptophan when the reversions were neutral. The overall mutation rate, as determined from the rates of mutation to valine resistance and to constitutive expression of the lac operon, did not increase during tryptophan starvation. The trp reversion rate did not increase when the cells were starved for cysteine for a similar period, indicating that the increased reversion rate was specific to conditions where the reversions were advantageous. Two artifactual explanations for the observations, delayed growth of some preexisting revertants and cryptic growth by some cells at the expense of dying cells within aged colonies, were tested and rejected as unlikely. The trp+ reversions that occurred while trp- colonies aged in the absence of tryptophan were shown to be time-dependent rather than replication-dependent, and it is suggested that they occur by mechanisms different from those that have been studied in growing cells. A heuristic model for the molecular basis of such mutations is proposed and evidence consistent with that model is discussed. It is suggested that the results in this and previous studies can be explained on the basis of underlying random mechanisms that act during prolonged periods of physiological stress, and that "directed" mutations are not necessarily the basis of those observations.
 ...
PMID:Spontaneous point mutations that occur more often when advantageous than when neutral. 222 88

Bacteria are especially useful as systems to study the molecular basis of adaptive evolution. Selection for novel metabolic capabilities has allowed us to study the evolutionary potential of organisms and has shown that there are three major "strategies" for the evolution of new metabolic functions. (i) Regulatory mutations may allow a gene to be expressed under unusual conditions. If the product of that gene is already active toward a novel resource, then a regulatory mutation alone may confer a new metabolic capability. (ii) Structural gene mutations may alter the catalytic properties of enzymes so that they can act on novel substrates. These structural gene mutations may dramatically improve catalytic capabilities, and in some cases they can confer entirely new capabilities upon enzymes. In most cases both regulatory and structural gene mutations are required for the effective evolution of new metabolic functions. (iii) Operons that are normally silent, or cryptic, may be activated by either point mutations or by the action of mobile genetic elements. When activated, these operons can provide entirely new pathways for the metabolism of novel resources. Selection can also play a role in modulating the probability that a particular adaptive mutation will occur. In this paper I present evidence that a specific adaptive mutation, reversion of the metB1 mutation, occurs 60 to 80 times more frequently during prolonged selection on plates under conditions where the members of the population are not growing than it does in growing cells under nonselective conditions. This selective condition, methionine starvation, does not increase the frequency of other mutations unrelated to methionine biosynthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Selection, adaptation, and bacterial operons. 268 97

Substrate-accelerated death was studied in lactose-limited cultures of Escherichia coli WP2 trp- and E. coli WP2 trp+. During starvation of E. coli WP2 trp- the viable count decreased while the number of trp+ revertants increased. Addition of 7.5 mM-cAMP to the starvation medium prevented the death of the trp-cells but not the increase in the number of trp+ revertants. As starvation of pure cultures of trp+ revertants did not result in death it suggests that the level of cAMP in trp- cells was lower that in trp+ cells. Addition of benzyl penicillin, nalidixic acid, novobiocin or rifampicin did not affect the viable counts thus indicating that neither cryptic growth not DNA replication occurred; however, in the presence of novobiocin there was no increase in the number of trp+ revertants. The possibility of a constitutive error-prone DNA repair mechanism is considered.
 ...
PMID:Mutation in Escherichia coli during substrate-accelerated death. 626 75

In a typical Escherichia coli K-12 culture starved for glucose, 50% of the cells lose viability in ca. 6 days (Reeve et al., J. Bacteriol. 157:758-763, 1984). Inhibition of protein synthesis by chloramphenicol resulted in a more rapid loss of viability in glucose-starved E. coli K-12 cultures. The more chloramphenicol added (i.e., the more protein synthesis was inhibited) and the earlier during starvation it was added, the greater was its effect on culture viability. Chloramphenicol was found to have the same effect on a relA strain as on an isogenic relA+ strain of E. coli. Addition of the amino acid analogs S-2-aminoethylcysteine, 7-azatryptophan, and p-fluorophenylalanine to carbon-starved cultures to induce synthesis of abnormal proteins had an effect on viability similar to that observed when 50 micrograms of chloramphenicol per ml was added at zero time for starvation. Both chloramphenicol and the amino acid analogs had delayed effects on viability, compared with their effects on synthesis of normal proteins. The need for protein synthesis did not arise from cryptic growth, since no cryptic growth of the starving cells was observed under the conditions used. From these and previous results obtained from work with peptidase-deficient mutants of E. coli K-12 and Salmonella typhimurium LT2 (Reeve et al., J. Bacteriol. 157:758-763, 1984), we concluded that a number of survival-related proteins are synthesized by E. coli K-12 cells as a response to carbon starvation. These proteins are largely synthesized during the early hours of starvation, but their continued activity is required for long-term survival.
 ...
PMID:Role of protein synthesis in the survival of carbon-starved Escherichia coli K-12. 638 5

Dithiothreitol (DTT) extraction of N-acetylglucosaminidase and trehalase from intact Candida albicans ATCC 10261 cells was monitored as an index of cell envelope porosity during N-acetylglucosamine-induced morphogenesis. Trehalase, which is secreted into the cell envelope during starvation and bud-formation, displayed similar extraction kinetics in starved, germ tube-forming, and bud-forming cells, indicating that the mother cell wall remains largely unchanged during morphogenic outgrowth and that the porosity of bud and mother cell walls is similar. N-acetylglucosaminidase, which is secreted specifically during morphogenesis, was released eightfold more rapidly from germ tube-forming than bud-forming cells, reflecting major differences in porosity between bud and germ tube. In addition, by assaying DTT extracts and extracted cell residues, it was found that the total extracellular N-acetylglucosaminidase activity increased 2- to 2.5-fold during DTT treatment. Thus, DTT unmasks a cryptic form of N-acetylglucosaminidase. The cryptic activity was associated with the cell wall fraction.
 ...
PMID:Differential extraction of N-acetylglucosaminidase and trehalase from the cell envelope of Candida albicans. 755 68

The iron starvation-induced, 2,042-amino-acid protein HMWP2 of Yersinia enterocolitica has two internal hydrophobic segments which might promote its export and association with the cytoplasmic membrane. To determine whether part of HMWP2 could be exported beyond the periplasmic face of the cytoplasmic membrane, we used TnphoA mutagenesis to construct 10 hybrid proteins in which periplasmic alkaline phosphatase (PhoA) was fused to the end of C-terminally truncated HMWP1 (at amino acid positions 1751 and 1753 two independent isolates]) had high alkaline phosphate activity (close to that of the native enzyme), both in Escherichia coli and in Y. pseudotuberculosis, indicating that the PhoA segment of the hybrid reached the periplasm. Deletion studies showed that the export signal resides in the second hydrophobic segment of HMWP2. This result would be compatible with the topology of the protein in the cytoplasmic membrane predicted from the distribution of charged amino acids at either end of the two hydrophobic segments. However, two hybrids in which the junction was even further toward the C terminus of HMMWP2 (at positions 1793 and 1999) had only weak alkaline phosphatase activity, suggesting that the predicted topology is incorrect. The location of HMWP2 was therefore determined by subcellular fractionation. The results indicate that HMPW2 is mainly cytoplasmic, consistent with its presumed role in the ATP-dependent, nonribosomal synthesis of an unknown peptide. We propose that the high alkaline phosphatase activity associated with some of the HMWP-2-PhoA hybrids results from the unmasking of the cryptic export signal activity in the second hydrophobic segment of HMPW2.
 ...
PMID:Yersinia spp. HMWP2, a cytosolic protein with a cryptic internal signal sequence which can promote alkaline phosphatase export. 789 1


1 2 3 4 5 6 Next >>