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PubMed1976

Mutations affecting catabolite repression of the L-arabinose regulon in Escherichia coli B/r.

Expression of the L-arabinose regulon in Escherichia coli B/r requires, among other things, cyclic adenosine-3', 5'-monophosphate (cAMP) and the cAMP receptor protein (CRP). Mutants deficient in adenyl cyclase (cya-), the enzyme which synthesizes cAMP, or CRP (crp-) are unable to utilize a variety of carbohydrates, including L-arabinose. Ara+ revertants of a cya-crp- strain were isolated on 0.2% minimal L-arabinose plates, conditions which require the entire ara regulon to be activated in the absence of cAMP and CRP. Evidence from genetic and physiological studies is consistent with placing these mutations in the araC regulatory gene. Deletion mapping with one mutant localized the site within either araO or araC, and complementation tests indicated the mutants acted trans to confer the ability to utilize L-arabinose in a cya-crp- genetic background. Since genetic analysis supports the conclusion, that the mutant sites are in the araC regulatory gene, the mutants were designated araCi, indicating a mutation in the regulatory gene affecting the cAMP-CRP requirement. Physiological analysis of one mutant, araCi1, illustrates the trans-acting nature of the mutation. In a cya-crp- genetic background, araCi1 promoted synthesis of both isomerase, a product of the araBAD operon, and permease, a product of the araE operon. Isomerase and permease levels in araCi1 cya+ crp+ were hyperinducible, and the sensitivity of each to cAMP was altered. Two models are presented that show the possible mutational lesion in the araCi strains.

Adenylyl Cyclases↗
PubMed1978

Molecular events during the release of delta-aminolevulinate dehydratase from catabolite repression.

Transfer of exponential-phase cells of Saccharomyces cerevisiae, previously grown in 2% glucose, to a derepression medium resulted in a prompt increase in the level of delta-aminolevulinate dehydratase, the rate-limiting enzyme of heme biosynthesis under these conditions. This derepression exhibited a lag of 35 min at 23 degrees C and required the participation of both RNA and protein syntheses. Dissection of the molecular events during this lag period disclosed that RNA synthesis, rnal gene function (messenger RNA transport from nucleus to cytosol), and initiation of protein synthesis were completed within less than 10, 18, and 24 min, respectively. The potential regulation of derepression by mitochondrial gene products and mitochondrial function was probed by means of a series of isogenic, respiration-deficient (rho-, pet-, and mit-) mutants; no such regulation was found.

Enzyme Repression↗
PubMed1981

Catabolite repression of Escherichia coli heat-stable enterotoxin activity.

The Escherichia coli heat-stable enterotoxin (ST) coded for by plasmid pYK007 (Apr ST+) showed a dependence for cyclic adenosine 3',5'-monophosphate (cAMP) to express ST activity in an adenyl cyclase (cya) deletion mutant; no ST activity was detected in the presence of cAMP in a cAMP receptor protein (crp) deletion mutant or in a double deletion mutant (delta cya delta crp). The cya-crp effect on ST activity could not be accounted for by a modification of the copy number of plasmid deoxyribonucleic acid per chromosome equivalent or by an alteration in the secretion of an active intracellular enterotoxin.

Bacterial Toxins↗
PubMed1983

Recessive mutations conferring resistance to carbon catabolite repression of galactokinase synthesis in Saccharomyces cerevisiae.

A total of 37 recessive mutations showing enhanced resistance to the glucose repression of galactokinase synthesis have been isolated by a selection procedure with a GAL81 gal7 double mutant. These mutations were grouped into three different complementation classes. One class, reg1, contains mutants arising from mutations at a site close to, but complementing, the gal3 locus. The reg1 mutant also showed resistance to the glucose repression of invertase synthesis but not to that of alpha-D-glucosidase. The two other classes were identified as arising from recessive mutations at the GAL82 locus and the GAL83 locus, respectively, at which various dominant mutations were isolated previously. When in a constitutive background due to the GAL81 or gal80 mutation, the GAL82 and GAL83 mutations did not show a mutually additive effect on the resistance to glucose repression of galactokinase synthesis, while the reg1 and GAL82 (or GAL83) mutations did. Based upon the specific behavior of cells with various genotypes for the above genes in response to the concentration of galactose and glucose in the medium, we propose a model involving three independent circuits for glucose signals in the regulation of the structural genes for the galactose pathway enzymes.

Drug Resistance, Microbial↗
PubMed1989

Transcription of pfl is regulated by anaerobiosis, catabolite repression, pyruvate, and oxrA: pfl::Mu dA operon fusions of Salmonella typhimurium.

Pyruvate formate-lyase (EC 2.3.1.54), a key enzyme in the anaerobic metabolism of Salmonella typhimurium, catalyzes the conversion of pyruvate to acetyl coenzyme A and formate. pfl::Mu dA operon fusions were isolated for the study of transcriptional regulation. pfl was transcribed both aerobically and anaerobically, but the activity increased about sixfold under anaerobic conditions. The addition of pyruvate, formate, and acetate in nutrient broth did not have any effect on the anaerobic expression of pfl. However, the addition of pyruvate to minimal glucose medium increased the anaerobic expression of pfl. The expression of pfl varied in different growth media. Anaerobic expression of pfl was lower when the culture was grown in minimal glucose medium than when it was grown in nutrient broth. When Casamino Acids (Difco Laboratories, Detroit, Mich.) were added to minimal glucose medium, the expression of pfl increased proportionally with the amount of Casamino Acids added. The transcription of pfl was positively controlled by the oxrA gene product and was affected by both the cya and crp mutations. However, mutations in genes affecting the cyclic AMP-cyclic AMP receptor protein complex or oxrA could not completely abolish the anaerobic derepression of pfl. In merodiploid strains, pfl::Mu dA/F' pfl+, the beta-galactosidase activities were decreased. The mutations gyrA, oxrC, and oxrE, which affected anaerobic metabolism, did not affect anaerobic expression of pfl.

Acetyltransferases↗
PubMed1993

Glucose uptake and catabolite repression in dominant HTR1 mutants of Saccharomyces cerevisiae.

Growth and carbon metabolism in triosephosphate isomerase (delta tpi1) mutants of Saccharomyces cerevisiae are severely inhibited by glucose. By using this feature, we selected for secondary site revertants on glucose. We defined five complementation groups, some of which have previously been identified as glucose repression mutants. The predominant mutant type, HTR1 (hexose transport regulation), is dominant and causes various glucose-specific metabolic and regulatory defects in TPI1 wild-type cells. HTR1 mutants are deficient in high-affinity glucose uptake and have reduced low-affinity transport. Transcription of various known glucose transporter genes (HXT1, HXT3, and HXT4) was defective in HTR1 mutants, leading us to suggest that HTR mutations affect a negative factor of HXT gene expression. By contrast, transcript levels for SNF3, which encodes a component of high-affinity glucose uptake, were unaffected. We presume that HTR1 mutations affect a negative factor of HXT gene expression. Multicopy expression of HXT genes or parts of their regulatory sequences suppresses the metabolic defects of HTR1 mutants but not their derepressed phenotype at high glucose concentrations. This suggests that the glucose repression defect is not a direct result of the metabolically relevant defect in glucose transport. Alternatively, some unidentified regulatory components of the glucose transport system may be involved in the generation or transmission of signals for glucose repression.

Blotting, Northern↗
PubMed1994

Inducibility of the TOL catabolic pathway in Pseudomonas putida (pWW0) growing on succinate in continuous culture: evidence of carbon catabolite repression control.

The TOL catabolic genes in Pseudomonas putida (pWW0) are clustered in the upper operon, encoding enzymes for the conversion of toluene and xylenes to benzoate and toluates, and the meta-cleavage operon, encoding enzymes for the conversion of the benzoate and toluates to tricarboxylic acid cycle intermediates. In this study, it was shown that cells growing in a chemostat under succinate growth-limiting conditions express both the upper and meta-cleavage pathways in response to o-xylene, a nonmetabolizable effector of the XylR regulatory protein. The dilution rate maintained in the succinate-limited chemostat cultures influenced the synthesis levels of TOL pathway enzymes, their steady-state levels, and their turnover rates. Cells growing in the presence of nonlimiting concentrations of succinate in continuous culture did not express pathway enzymes in response to the addition of o-xylene, which was due to a blockage at the transcriptional level. Expression of the meta-cleavage pathway in response to 2,3-dimethylbenzoate, a nonmetabolizable effector of the XylS regulatory protein, was 93% lower in cultures exposed to succinate at nonlimiting concentrations than in the succinate-limited chemostats. The mRNA level of xylS during nonlimited growth on succinate was very low compared with that in succinate-limited cultures, suggesting that suppression of expression of the meta-cleavage pathway is regulated mainly by the level of the XylS regulator.

Base Sequence↗
PubMed1995

The HPr protein of the phosphotransferase system links induction and catabolite repression of the Bacillus subtilis levanase operon.

The LevR protein is the activator of expression of the levanase operon of Bacillus subtilis. The promoter of this operon is recognized by RNA polymerase containing the sigma 54-like factor sigma L. One domain of the LevR protein is homologous to activators of the NtrC family, and another resembles antiterminator proteins of the BglG family. It has been proposed that the domain which is similar to antiterminators is a target of phosphoenolpyruvate:sugar phosphotransferase system (PTS)-dependent regulation of LevR activity. We show that the LevR protein is not only negatively regulated by the fructose-specific enzyme IIA/B of the phosphotransferase system encoded by the levanase operon (lev-PTS) but also positively controlled by the histidine-containing phosphocarrier protein (HPr) of the PTS. This second type of control of LevR activity depends on phosphoenolpyruvate-dependent phosphorylation of HPr histidine 15, as demonstrated with point mutations in the ptsH gene encoding HPr. In vitro phosphorylation of partially purified LevR was obtained in the presence of phosphoenolpyruvate, enzyme I, and HPr. The dependence of truncated LevR polypeptides on stimulation by HPr indicated that the domain homologous to antiterminators is the target of HPr-dependent regulation of LevR activity. This domain appears to be duplicated in the LevR protein. The first antiterminator-like domain seems to be the target of enzyme I and HPr-dependent phosphorylation and the site of LevR activation, whereas the carboxy-terminal antiterminator-like domain could be the target for negative regulation by the lev-PTS.

Amino Acid Sequence↗
PubMed1999

Cyclic AMP can decrease expression of genes subject to catabolite repression in Saccharomyces cerevisiae.

External cyclic AMP (cAMP) hindered the derepression of gluconeogenic enzymes in a pde2 mutant of Saccharomyces cerevisiae, but it did not prevent invertase derepression. cAMP reduced nearly 20-fold the transcription driven by upstream activation sequence (UAS1FBP1) from FBP1, encoding fructose-1,6-bisphosphatase; it decreased 2-fold the activation of transcription by UAS2FBP1. Nuclear extracts from cells derepressed in the presence of cAMP were impaired in the formation of specific UASFBP1-protein complexes in band shift experiments. cAMP does not appear to act through the repressing protein Mig1. Control of FBP1 transcription through cAMP is redundant with other regulatory mechanisms.

Carboxy-Lyases↗
PubMed2000

Isolation of the MIG1 gene from Candida albicans and effects of its disruption on catabolite repression.

We have cloned a Candida albicans gene (CaMIG1) that encodes a protein homologous to the DNA-binding protein Mig1 from Saccharomyces cerevisiae (ScMig1). The C. albicans Mig1 protein (CaMig1) differs from ScMig1, in that, among other things, it lacks a putative phosphorylation site for Snf1 and presents several long stretches rich in glutamine or in asparagine, serine, and threonine and has the effector domain located at some distance (50 amino acids) from the carboxy terminus. Expression of CaMIG1 was low and was similar in glucose-, sucrose-, or ethanol-containing media. Disruption of the two CaMIG1 genomic copies had no effect in filamentation or infectivity. Levels of a glucose-repressible alpha-glucosidase, implicated in both sucrose and maltose utilization, were similar in wild-type or mig1/mig1 cells. Disruption of CaMIG1 had also no effect on the expression of the glucose-repressed gene CaGAL1. CaMIG1 was functional in S. cerevisiae, as judged by its ability to suppress the phenotypes produced by mig1 or tps1 mutations. In addition, CaMig1 formed specific complexes with the URS1 region of the S. cerevisiae FBP1 gene. The existence of a possible functional analogue of CaMIG1 in C. albicans was suggested by the results of band shift experiments.

Amino Acid Sequence↗
PubMed2002

Catabolite repression of Escherichia coli biofilm formation.

Biofilm formation was repressed by glucose in several species of Enterobacteriaceae. In Escherichia coli, this effect was mediated at least in part by cyclic AMP (cAMP)-cAMP receptor protein. A temporal role for cAMP in biofilm development was indicated by the finding that glucose addition after approximately 24 h failed to repress and generally activated biofilm formation.

Biofilms↗
PubMed1981

Isolation and characterization of dominant mutations resistant to carbon catabolite repression of galactokinase synthesis in Saccharomyces cerevisiae.

Seven dominant mutations showing greatly enhanced resistance to the glucose repression of galactokinase synthesis have been isolated from GAL81 mutants, which have the constitutive phenotype but are still strongly repressible by glucose for the synthesis of the Leloir enzymes. These glucose-resistant mutants were due to semidominant mutations at either of two loci, GAL82 and GAL83. Both loci are unlinked to the GAL81- gal4, gal80, or gal7 X gal10 X gal1 locus or to each other. The GAL83 locus was mapped on chromosome V at a site between arg9 and cho1. The GAL82 and GAL83 mutations produced partial resistance of galactokinase to glucose repression only when one or both of these mutations were combined with a GAL81 or a gal80 mutation. The GAL82 and GAL83 mutations are probably specific for expression of the Leloir pathway and related enzymes, because they do not affect the synthesis of alpha-D-glucosidase, invertase, or isocitrate lyase.

Galactokinase↗