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At least 73 records · Page 4Linked to original sources
PubMed1988

Regulation of the galactose-inducible lac operon and the histidine utilization operons in pts mutants of Klebsiella aerogenes.

Galactose appears to be the physiological inducer of the chromosomal lac operon in Klebsiella aerogenes. Both lactose and galactose are poor inducers in strains having a functional galactose catabolism (gal) operon, but both are excellent inducers in gal mutants. Thus the slow growth of K. aerogenes on lactose reflects the rapid degradation of the inducer. Several pts mutations were characterized and shown to affect both inducer exclusion and permanent catabolite repression. The beta-galactosidase of pts mutants cannot be induced at all by lactose, and pts mutants appear to have a permanent and constitutive inducer exclusion phenotype. In addition, pts mutants show a reduced rate of glucose metabolism, leading to slower growth on glucose and a reduced degree of glucose-mediated permanent catabolite repression. The crr-type pseudorevertants of pts mutations relieve the constitutive inducer exclusion for lac but do not restore the full level of glucose-mediated permanent catabolite repression and only slightly weaken the glucose-mediated inducer exclusion. Except for weakening the glucose-mediated permanent catabolite repression, pts and crr mutations have no effect on expression of the histidine utilization (hut) operons.

Ammonia-Lyases↗
PubMed1988

cis-acting sites in the transcript of the Bacillus subtilis trp operon regulate expression of the operon.

Transcription of the trp operon of Bacillus subtilis is regulated by attenuation. A trpE'-'lacZ gene fusion preceded by the wild-type trp promoter-leader region was used to analyze regulation. Overproduction of the trp leader transcript in trans from a multicopy plasmid caused constitutive expression of the chromosomal trpE'-'lacZ fusion, presumably by titrating a negative regulatory factor encoded by the mtr locus. Subsegments of the trp leader region cloned onto the multicopy plasmid were examined for their abilities to elevate beta-galactosidase activity. An RNA segment spanning the portion of the leader transcript that forms the promoter-proximal strand of the proposed antiterminator structure was most active in this trans test. The data suggest that the mtr gene product, when activated by tryptophan, binds to this RNA segment and prevents formation of the antiterminator. In this manner, the trans-acting factor promotes formation of the RNA structure that causes transcription termination. Secondary-structure predictions for the leader segment of the trp operon transcript suggest that if the mtr factor bound this RNA segment in a nonterminated transcript, the ribosome-binding site for the first structural gene, trpE, could be sequestered in a stable RNA structure. We tested this possibility by comparing transcriptional and translational fusions containing the initial segments of the trp operon. Our findings suggest that the mtr product causes both transcription attenuation and inhibition of translation of trpE mRNA. Inhibition of translation initiation would reduce ribosome density on trpE mRNA, perhaps making it more labile. Consistent with this interpretation, the addition of tryptophan to mtr+ cultures increased the rate of trpE'-'lacZ mRNA decay.

Bacillus subtilis↗
PubMed1993

Gene components responsible for discrete substrate specificity in the metabolism of biphenyl (bph operon) and toluene (tod operon).

bph operons coding for biphenyl-polychlorinated biphenyl degradation in Pseudomonas pseudoalcaligenes KF707 and Pseudomonas putida KF715 and tod operons coding for toluene-benzene metabolism in P. putida F1 are very similar in gene organization as well as size and homology of the corresponding enzymes (G. J. Zylstra and D. T. Gibson, J. Biol. Chem. 264:14940-14946, 1989; K. Taira, J. Hirose, S. Hayashida, and K. Furukawa, J. Biol. Chem. 267:4844-4853, 1992), despite their discrete substrate ranges for metabolism. The gene components responsible for substrate specificity between the bph and tod operons were investigated. The large subunit of the terminal dioxygenase (encoded by bphA1 and todC1) and the ring meta-cleavage compound hydrolase (bphD and todF) were critical for their discrete metabolic specificities, as shown by the following results. (i) Introduction of todC1C2 (coding for the large and small subunits of the terminal dioxygenase in toluene metabolism) or even only todC1 into biphenyl-utilizing P. pseudoalcaligenes KF707 and P. putida KF715 allowed them to grow on toluene-benzene by coupling with the lower benzoate meta-cleavage pathway. Introduction of the bphD gene (coding for 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase) into toluene-utilizing P. putida F1 permitted growth on biphenyl. (ii) With various bph and tod mutant strains, it was shown that enzyme components of ferredoxin (encoded by bphA3 and todB), ferredoxin reductase (bphA4 and todA), and dihydrodiol dehydrogenase (bphB and todD) were complementary with one another. (iii) Escherichia coli cells carrying a hybrid gene cluster of todClbphA2A3A4BC (constructed by replacing bphA1 with todC1) converted toluene to a ring meta-cleavage 2-hydroxy-6-oxo-hepta-2,4-dienoic acid, indicating that TodC1 formed a functional multicomponent dioxygenase associated with BphA2 (a small subunit of the terminal dioxygenase in biphenyl metabolism), BphA3, and BphA4.

Base Sequence↗
PubMed1997

Expression and control of an operon from an intracellular symbiont which is homologous to the groE operon.

Members of the genus Buchnera are intracellular symbionts harbored by the aphid bacteriocyte which selectively synthesize symbionin, a homolog of the Escherichia coli GroEL protein, in vivo. Symbionin and SymS, a GroES homolog, are encoded in the symSL operon. Northern blotting and primer extension analyses revealed that the symSL operon invariably gives rise to a bicistronic mRNA under the control of a heat shock promoter, though the amount of the symSL mRNA in the isolated symbiont did not increase in response to heat shock. The sigma32 protein that recognizes the heat shock promoter in E. coli was scarcely detected in Buchnera cells even after heat shock. Although the functionally essential regions of the Buchnera sigma32 protein were well conserved, the Buchnera rpoH gene did not complement an E. coli delta rpoH mutant. On the one hand, the A-T evolutionary pressure imposed on the Buchnera genome may have not only decreased the activity of its sigma32 but also ruined the nucleotide sequences necessary for the expression of rpoH; on the other hand, it may have facilitated expression of the symSL operon without activation by sigma32.

Amino Acid Sequence↗
PubMed1995

The gtcRS operon coding for two-component system regulatory proteins is located adjacent to the grs operon of Bacillus brevis.

We identified, cloned and sequenced an operon comprising of two genes gtcR and gtcS located adjacent to the grs operon of Bacillus brevis, which encodes the multienzymes involved in the biosynthesis of the peptide antibiotic gramicidin S. The transcription initiation site of the gtcRS operon was determined in Bacillus brevis and Bacillus subtilis. The encoded proteins GtcR and GtcS were identified as members of the two-component system family of signal transducing proteins.

Amino Acid Isomerases↗
PubMed1983

[Functioning of amino acid operons in Escherichia coli strains with an altered transcription and translation apparatus. I. The effect of mutations in gene rpsL coding ribosomal protein S12 on the functioning of the ilv operon].

Derepression of the ilv operon in rel strains of Escherichia coli is delayed when cells are transferred from rich to minimal medium and is completely blocked when the mixture of amino acids--serine, methionine and glycine is present in the minimal medium. It is shown that alterations in translation machinery caused by streptomycine resistance mutation can also lead to the delay of the ilv operon derepression in rel+ strains or to its complete inhibition in rel strains of E. coli. The possible mechanisms of high sensitivity of the ilv operon to different alterations in E. coli are discussed.

Amino Acids↗
PubMed1983

[Expression of the amino acid operons in Escherichia coli strains with an altered transcription and translation apparatus. III. The effect of mutations in the rpoB gene coding for the beta-subunit of RNA-poly-merase on ilv-operon expression].

The influence of rifampicin resistance mutations on expression of the ilv operon of Escherichia coli was investigated. Some of these mutations, like those previously described in our works, occur in translation machinery of E. coli and inhibit derepression of the ilv operon. However, another group of mutations stimulated the expression of the operon when mutated cells were transferred from rich to minimal growth medium. The possible mechanisms of the effects of rifampicin resistance mutations on the action of coupled transcription--translation system are discussed.

Amino Acids↗
PubMed1983

[Expression of the amino acid operons in Escherichia coli strains with an altered transcription and translation apparatus. IV. The effect of mutations disturbing the coupling of the transcription and translation processes on ilv-operon expression in cells carrying the mutation in the spoT gene].

The rate of adaptation of Escherichia coli K-12 NF930 spoT1 cells with elevated intracellular level of ppGpp to various minimal media was studied. It has been found that the rate of adaptation of spoT cells, like that of parent and rel strains, depends mainly on the rate of derepression of the ilv operon. The maximal rate of the ilv operon derepression was observed when an optimal concentration of ppGpp was maintained in cells. Derepression of the ilv operon is sharply delayed when the level of ppGpp is elevated or reduced. Mutations altering the translation system do not change the rate of adaptation of spoT cells. Rifampicin resistance mutations which altered the structure of RNA polymerase change the rate of adaptation of spoT cells to minimal media, especially to those containing serine at high concentrations. The possible role of serine in the regulation of ppGpp degradation system is discussed.

Adaptation, Physiological↗
PubMed1980

[Funtional study of gene relA in the expression of amino acid operons. III. The effect of the allelic state of gene relA on the derepression of the threonine and isoleucine-valine operons of Escherichia coli K-12].

During the derepression of threonine and isoleucine-valine operons the increase of activity of homoserine dehydrogenase and threonine deaminase respectively occurs only in relA+ strains of Escherichia coli K-12, while the activity of these enzymes in relA mutants does not change. The increase of the activity of homoserine dehydrogenase in relA+ strains corresponds to the increase of the fraction of the thr-mRNA, i.e. the expression of threonine operon is regulated at the level of transcription. After isoleucine is exhausted, only relA+ cells of threonine producer MG442 increase homoserine dehydrogenase activity and production of threonine. Thus, the regulation of transcription and translation of threonine and isoleucine-valine operons depends upon the allelic state of the relA gene.

Alleles↗
PubMed1981

Regulation of the S10 ribosomal protein operon in E. coli: nucleotide sequence at the start of the operon.

We have determined the DNA sequence of a 1250 base pair segment of the Escherichia coli chromosome that carries the promoter for the S10 ribosomal protein operon, the S10 gene and part of the L3 gene. A DNA fragment carrying the putative S10 promoter was cloned into the plasmid mini-Col E1, which contains a transcription termination signal close to the single Hind II site. Cells harboring the hybrid plasmid produced a relatively stable hybrid mRNA with the expected sequence, demonstrating that the promoter functions in vivo. Comparison of the mRNA sequence around the start of the S10 coding region, the presumed target site for L4 repressor protein, with the known binding site for L4 on 23S rRNA revealed the presence of sequence homologies. This supports the model of the translational feedback regulation of the S10 operon by L4.

Bacterial Proteins↗
PubMed1985

Nucleotide sequence of the rpsU-dnaG-rpoD operon from Salmonella typhimurium and a comparison of this sequence with the homologous operon of Escherichia coli.

In Escherichia coli the genes encoding ribosomal protein S21 (rpsU), DNA primase (dnaG), and the 70-kDal sigma subunit of RNA polymerase (rpoD) are contained in a single operon. These gene products are involved in the initiation of translation, DNA replication, and transcription, respectively. We have examined the homologous region in the closely related bacterium Salmonella typhimurium and have found that the same three genes are similarly organized. We have sequenced the DNA for this operon in S. typhimurium and have compared the (nt) nucleotide and amino acid (aa) sequences with E. coli. In the coding regions, the sequence conservation varies from extremely high for rpsU to moderate for dnaG with respect to both nt and aa sequence. In the noncoding regions, sequences thought to be important for the regulation of transcription are conserved, while other sequences are not conserved. aa differences in DNA primase and sigma are not randomly distributed and suggest regions that may be important for protein structure or function.

Amino Acid Sequence↗
PubMed2004

Modeling operon dynamics: the tryptophan and lactose operons as paradigms.

Understanding the regulation of gene control networks and their ensuing dynamics will be a critical component in the understanding of the mountain of genomic data being currently collected. This paper reviews recent mathematical modeling work on the tryptophan and lactose operons which are, respectively, the classical paradigms for repressible and inducible operons.

Escherichia coli↗
PubMed2005

Estimation of ribosomal RNA operon (rrn) copy number in Acinetobacter isolates and potential of patterns of rrn operon-containing fragments for typing strains of members of this genus.

The copy number of the rrn operon in 70 strains of Acinetobacter including the type strains of almost all the genomic species with validated names was estimated after digestion of their genomic DNA by the restriction enzymes BglII and PstI, and Southern blotting. Copy number estimates varied between and among species, with between 3 and 7 rrn operon copies detected. Copy number estimates obtained from the same strain with the two enzymes sometimes varied. BglII generated RFLP patterns of the rrn containing fragments obtained from Southern blots after agarose gel electrophoresis were examined for their value in identifying Acinetobacter isolates. This method was very reproducible with the same fragment pattern always generated from the same isolate on repeated analysis. Often multiple strains of the same genomic species gave identical or very similar patterns (e.g. Acinetobacter baylyi), clustering closest together on the dendrogram generated after numerical analysis of these patterns. However, with some, like BG5 and BG8, the patterns derived from the different strains, some of which had been placed in this genomic species from DNA:DNA hybridization data, varied considerably to each other and to the type strain. Little similarity was seen when relationships between these strains based on these patterns were compared to those using DNA:DNA hybridization data. Often these patterns could be used to question earlier identification of strains using phenotypic characters. Thus, strain AB82 thought to belong to genomic species 5 gave an identical pattern to A. bouvetii(T) (DSM 14964). In some cases this pattern analysis suggested that novel species of Acinetobacter might exist among the strains examined.

Acinetobacter↗
PubMed1998

Transcriptional activation of the glycolytic las operon and catabolite repression of the gal operon in Lactococcus lactis are mediated by the catabolite control protein CcpA.

The Lactococcus lactis ccpA gene, encoding the global regulatory protein CcpA, was identified and characterized. Northern blot and primer extension analyses showed that the L. lactis ccpA gene is constitutively transcribed from a promoter that does not contain a cre sequence. Inactivation of the ccpA gene resulted in a twofold reduction in the growth rate compared with the wild type on glucose, sucrose and fructose, while growth on galactose was almost completely abolished. The observed growth defects could be complemented by the expression of either the L. lactis or the Bacillus subtilis ccpA gene. The disruption of the ccpA gene reduced the catabolite repression of the gal operon, which contains a cre site at the transcription start site and encodes enzymes involved in galactose catabolism. In contrast, CcpA activates the transcription of the cre-containing promoter of the las operon, encoding the glycolytic enzymes phosphofructokinase, pyruvate kinase and L-lactate dehydrogenase, because its transcription level was fourfold reduced in the ccpA mutant strain compared with the wild-type strain. The lower activities of pyruvate kinase and L-lactate dehydrogenase in the ccpA mutant strain resulted in the production of metabolites characteristic of a mixed-acid fermentation, whereas the fermentation pattern of the wild-type strain was essentially homolactic.

Bacterial Proteins↗
PubMed1987

The narL gene product activates the nitrate reductase operon and represses the fumarate reductase and trimethylamine N-oxide reductase operons in Escherichia coli.

Escherichia coli, which can utilize O2, nitrate, fumarate, or trimethylamine N-oxide (Me3NO) as terminal electron acceptor, preferentially utilizes the one with the highest redox potential. Thus O2 prevents induction of nitrate, fumarate, and Me3NO reductases, and nitrate curtails the induction of fumarate and Me3NO reductases. Under anaerobic conditions the narL gene product, in the presence of nitrate, is known to activate transcription of the narC operon, which encodes nitrate reductase. This study shows that the same product plays a role in the repression by nitrate of the operons (frd and tor) that encode fumarate and Me3NO reductases. In contrast, the anaerobic repression of ethanol dehydrogenase by nitrate does not require the narL product. Expression of narL does not require the fnr gene product, a pleiotropic activator that is required for full expression of narC, frd, and tor.

Bacterial Proteins↗
PubMed1985

The sequence of the distal end of the E. coli ribosomal RNA rrnE operon indicates conserved features are shared by rrn operons.

The 1440 nucleotides of the distal region of the E. coli ribosomal RNA operon found on the lambda aroE transducing phage has been sequenced. We show that the lambda aroE hybrid rrn operon ends after a solitary 5S RNA gene with rrnE distal sequence. A single terminator structure of dyad symmetry followed by a run of six T's have been identified and compared to other sequenced rrn terminator hairpins. Immediately adjacent to the hairpin is a region of interrupted but conserved sequence that is shared by rrnE, rrnB and rrnD. An open reading frame of 127 amino acids abuts the terminator structure. Another open reading frame of 147 amino acids is found on the opposite strand several hundred nucleotides downstream.

Bacteriophage lambda↗
PubMed1999

Transcriptional regulation of molybdoenzyme synthesis in Escherichia coli in response to molybdenum: ModE-molybdate, a repressor of the modABCD (molybdate transport) operon is a secondary transcriptional activator for the hyc and nar operons.

Escherichia coli growing under anaerobic conditions produces several molybdoenzymes, such as formate hydrogenlyase (formate to H2 and CO2; hyc and fdhF genes) and nitrate reductase (narGHJI genes). Synthesis of these molybdoenzymes, even in the presence of the cognate transcriptional activators and effectors, requires molybdate in the medium. Besides the need for molybdopterin cofactor synthesis, molybdate is also required for transcription of the genes encoding these molybdoenzymes. In E. coli, ModE was previously identified as a repressor controlling transcription of the operon encoding molybdate transport components (modABCD). In this work, the ModE protein was also found to be a required component in the activation of hyc-lacZ to an optimum level, but only in the presence of molybdate. Mutant ModE proteins which are molybdate-independent for repression of modA-lacZ also restored hyc-lacZ expression to the wild-type level even in the absence of molybdate. Nitrate-dependent enhancement of transcription of narX-lacZ was completely abolished in a modE mutant. Nitrate-response by narG-lacZ and narK-lacZ was reduced by about 50% in a modE mutant. DNase I footprinting experiments revealed that the ModE protein binds the hyc promoter DNA in the presence of molybdate. ModE-molybdate also protected DNA in the intergenic region between narXL and narK from DNase I hydrolysis. DNA sequences (5' TAYAT 3' and 5' GTTA 3') found in ModE-molybdate-protected modABCD operator DNA were also found in the ModE-molybdate-protected region of hyc promoter DNA (5' GTTA-7 bp-CATAT 3') and narX-narK intergenic region (5' GTTA-7 bp-TACAT 3'). Based on these results, a working model is proposed in which ModE-molybdate serves as a secondary transcriptional activator of both the hyc and narXL operons which are activated primarily by the transcriptional activators, FhlA and NarL, respectively.

Anion Transport Proteins↗
PubMed2001

Construction of a series of mutants lacking all of the four major mex operons for multidrug efflux pumps or possessing each one of the operons from Pseudomonas aeruginosa PAO1: MexCD-OprJ is an inducible pump.

We constructed a series of deletion mutants lacking all of the four major mex operons for Mex multidrug efflux pumps or possessing each one of the operons from Pseudomonas aeruginosa PAO1. The drug specificity of MexAB-OprM, MexXY-OprM and MexCD-OprJ was investigated. Surprisingly, we found that the MexCD-OprJ was an inducible pump, inducers of which were tetraphenylphosphonium chloride, ethidium bromide, rhodamine 6G and acriflavine. Fluoroquinolones, chloramphenicol, erythromycin and tetracycline were not inducers although they were substrates of MexCD-OprJ.

Anti-Bacterial Agents↗