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PubMed1992

cis-acting regulatory elements involved in oxygen and light control of puc operon transcription in Rhodobacter sphaeroides.

Transcriptional expression of the puc operon in Rhodobacter sphaeroides is highly regulated by both oxygen and light. The approximately 600 bp of DNA upstream of the 5' ends of the two puc-specific transcripts encompasses two functionally separable cis-acting domains. The upstream regulatory region (URS) (-629 to -150) is responsible for enhanced transcriptional regulation of puc operon expression by oxygen and light. The more proximal upstream region (downstream regulatory region [DRS]), containing putative promoter(s), operator(s), and factor binding sites (-150 to -1), is involved in unenhanced transcriptional expression of the puc operon under aerobic and anaerobic conditions. Thus, the DRS shows normal derepression of puc operon expression when cells are shifted from aerobic to photosynthetic growth conditions in terms of percent change but does not show the potential range of expression that is only observed when elements of the URS are present. Because of these observations, we have made a distinction between anaerobic control (describing the shift) and oxygen control (describing the magnitude of derepression). Promoter(s) and/or activator function(s) of the puc operon is associated with a 35-bp DNA region between -92 and -57. Homologous sequences at -10 to -27 and -35 to -52 appear to involve additional regulatory elements: mutations at -12 (A to C) and -26 (G to A) result in partial derepression of puc operon expression under conditions of high aeration. Both point mutations require the upstream regulatory region (-629 to -150) to be present in cis for partial derepression of puc operon transcription under aerobic conditions. Immediately upstream of the promoter and/or activator region are overlapping consensus sequences for IHF (integratin host factor) and FNR (fumarate nitrate reductase) (-105 to -129). This region appears to be essential for enhanced expression of the puc operon. Thus, these two regulatory domains (URS and DRS) appear to involve approximately seven unique regulatory elements. In addition, the data reveal a direct interaction between the URS (-629 to -150) and the DRS (-150 to -1).

Anaerobiosis↗

PubMed1992

The products of the kdpDE operon are required for expression of the Kdp ATPase of Escherichia coli.

The expression of the Kdp system for K+ uptake in Escherichia coli requires the products of two genes, kdpD and kdpE. These genes constitute an operon adjacent to the kdpABC operon that encodes the three membrane protein subunits of Kdp. Both operons are transcribed in the same direction and overlap; the kdpDE promoter is in kdpC, the last gene of the kdpABC operon. Transcription of the kdpDE operon is at a low level when Kdp is not expressed; transcription increases about 10-fold when kdpABC is turned on, indicating significant read-through of the kdpDE operon by transcripts beginning at the promoter of kdpABC operon. The proximal region of the kdpD gene is the site of most mutations that lead to constitutive expression of the kdpABC operon.

Adenosine Triphosphatases↗

PubMed1993

In vivo regulatory responses of four Escherichia coli operons which encode leucyl-tRNAs.

Four Escherichia coli operons, the leuV operon which encodes tRNA(1Leu), the leuX operon which encodes tRNA(6Leu), the metT operon which encodes tRNA(3Leu), and the argT operon which encodes tRNA(1Leu), were examined for the stringent response induced by serine hydroxamate and for growth rate-dependent regulation. In nuclease protection assays, the leuV operon displayed the stringent response in response to leucine starvation, analog inhibition, and growth of a temperature-sensitive leucyl-tRNA synthetase mutant at nonpermissive temperatures. The leuV operon also exhibited the stringent response in multicopy plasmids. The promoters of all four leucyl operons were fused to the gene for beta-galactosidase and inserted into the chromosome by using bacteriophage lambda. All except the leuX promoter displayed growth rate-dependent regulation, consistent with the recent report that the concentration of tRNA(6Leu) actually decreases as growth rate increases. The leuV promoter fused to the beta-galactosidase gene showed a decrease in efficiency in the presence of extrachromosomal copies of rRNA genes. All chromosomal tRNA genes examined showed decreased transcriptional activity following a stringent response, but the leuX gene responded to a lesser extent (3-fold versus 10-fold or more) than the others. Primer extension analysis of this promoter showed little if any response to serine hydroxamate treatment, suggesting that multiple levels of control may exist or that promoter context effects are important in regulation.

Base Sequence↗

PubMed1993

Identification of a novel operon in Lactococcus lactis encoding three enzymes for lactic acid synthesis: phosphofructokinase, pyruvate kinase, and lactate dehydrogenase.

The discovery of a novel multicistronic operon that encodes phosphofructokinase, pyruvate kinase, and lactate dehydrogenase in the lactic acid bacterium Lactococcus lactis is reported. The three genes in the operon, designated pfk, pyk, and ldh, contain 340, 502, and 325 codons, respectively. The intergenic distances are 87 bp between pfk and pyk and 117 bp between pyk and ldh. Plasmids containing pfk and pyk conferred phosphofructokinase and pyruvate kinase activity, respectively, on their host. The identity of ldh was established previously by the same approach (R. M. Llanos, A. J. Hillier, and B. E. Davidson, J. Bacteriol. 174:6956-6964, 1992). Each of the genes is preceded by a potential ribosome binding site. The operon is expressed in a 4.1-kb transcript. The 5' end of the transcript was determined to be a G nucleotide positioned 81 bp upstream from the pfk start codon. The pattern of codon usage within the operon is highly biased, with 11 unused amino acid codons. This degree of bias suggests that the operon is highly expressed. The three proteins encoded on the operon are key enzymes in the Embden-Meyerhoff pathway, the central pathway of energy production and lactic acid synthesis in L. lactis. For this reason, we have called the operon the las (lactic acid synthesis) operon.

Amino Acid Sequence↗

PubMed1995

The dnaKJ operon of Agrobacterium tumefaciens: transcriptional analysis and evidence for a new heat shock promoter.

The dnaKJ operon of Agrobacterium tumefaciens was cloned and sequenced and was found to be highly homologous to previously analyzed dnaKJ operons. Transcription of this operon in A. tumefaciens was stimulated by heat shock as well as by exposure to ethanol and hydrogen peroxide. There were two transcripts representing the dnaKJ operon: one containing the dnaK and dnaJ genes and the second containing only the dnaK gene. Primer extension analysis indicated that transcription started from the same site in heat-shocked cells and in untreated cells. The upstream regulatory region of the dnaKJ operon of A. tumefaciens does not contain the highly conserved inverted repeat sequence previously found in the groESL operon of this bacterium, as well as in many other groE and dnaK operons. Sequence analysis of the promoter region of several groESL and dnaK operons from alpha-purple proteobacteria indicates the existence of a putative promoter sequence different from the known consensus promoter sequences recognized by the Escherichia coli vegetative or heat shock sigma factor. This promoter may constitute the heat shock promoter of these alpha-purple proteobacteria.

Agrobacterium tumefaciens↗

PubMed1997

Regulation of the dnaK operon of Streptomyces coelicolor A3(2) is governed by HspR, an autoregulatory repressor protein.

The dnaK operon of Streptomyces coelicolor contains four genes (5'-dnaK-grpE-dnaJ-hspR). The fourth gene encodes a novel heat shock protein, HspR, which appears so far to be unique to the high-G+C actinomycete group of bacteria. HspR binds with high specificity to three inverted repeat sequences in the promoter region of the S. coelicolor dnaK operon, strongly suggesting a direct role for HspR in heat shock gene regulation. Here we present genetic and biochemical evidence that HspR is the repressor of the dnaK operon. Disruption of hspR leads to high-level constitutive transcription of the dnaK operon. Parallel transcriptional analyses of groESL1 and groEL2 expression demonstrated that heat shock regulation of the groE genes was essentially unaffected in an hspR null mutant, although the basal (uninduced) level of groEL2 transcription was slightly elevated compared with the wild type. The results of HspR titration experiments, where the dnaK operon promoter region was cloned at ca. 50 copies per chromosome, were consistent with the prediction that HspR functions as a negative autoregulator. His-tagged HspR, overproduced and purified from Escherichia coli, was shown to repress transcription from the dnaK operon promoter in vitro, providing additional evidence for the proposal that HspR directly regulates transcription of the dnaK operon. These studies indicate that there are at least two transcriptional mechanisms for controlling heat shock genes in S. coelicolor--one controlling the dnaK operon and another controlling the groE genes.

Bacterial Proteins↗

PubMed1998

Transcription analysis of two disparate rRNA operons in the halophilic archaeon Haloarcula marismortui.

The genome of the halophilic archaeon Haloarcula marismortui contains two rRNA operons designated rrnA and rrnB. Genomic clones of the two operons and their flanking regions have been sequenced, and primary transcripts and processing intermediates derived from each operon have been characterized. The 16S, 23S, and 5S genes from the two operons were found to differ at 74 of 1,472 positions, 39 of 2,922 positions, and 2 of 122 positions, respectively. This degree of sequence divergence for multicopy (paralogous) rRNA genes was 10- to 50-fold or more higher than anticipated. The two operons exhibit other profound differences that include (i) the presence in rrnA and the absence in rrnB of tRNAAla and tRNACys genes in the intergenic and distal regions, respectively, (ii) divergent 5' flanking sequences, and (iii) distinct pathways for processing and maturation of 16S rRNA. Processing and maturation of 16S and 23S rRNA from rrnA operon transcripts and of 23S rRNA from rrnB operon transcripts follow the canonical halophilic pathway, whereas maturation of 16S rRNA from rrnB operon transcripts follows an unusual and different pathway that is apparently devoid of any 5' processing intermediate.

Base Sequence↗

PubMed1999

Regulation of expression of the Lactococcus lactis histidine operon.

In Lactococcus lactis, the his operon contains all the genes necessary for histidine biosynthesis. It is transcribed from a unique promoter, localized 300 bp upstream of the first gene. The region corresponding to the untranslated 5' end of the transcript, named the his leader region, displays the typical features of the T box transcriptional attenuation mechanism which is involved in the regulation of many amino acid biosynthetic operons and tRNA synthetase genes in gram-positive bacteria. Here we describe the regulation of transcription of the his operon by the level of histidine in the growth medium. In the absence of histidine, two transcripts are present. One covers the entire operon, while the other stops at a terminator situated about 250 bp downstream of the transcription start point. DNA sequences implicated in regulation of the his operon were identified by transcriptional fusion with luciferase genes and site-directed mutagenesis. In addition to the previously defined sequences necessary for effective T-box-mediated regulation, new essential regions were identified. Eighteen percent of the positions of the his leader region were found to differ in seven distantly related strains of L. lactis. Analysis of the variable positions supports the folding model of the central part of the his leader region. Lastly, in addition to the T-box-mediated regulation, the operon is regulated at the level of initiation of transcription, which is repressed in the presence of histidine. An operator site, necessary for full repression, overlaps the terminator involved in the T box attenuation mechanism. The functionality of the operator is altered on plasmids with low and high copy numbers, suggesting that supercoiling may play a role in the expression of the his operon. The extents of regulation at the levels of initiation and attenuation of transcription are 6- to 8-fold and 14-fold, respectively. Together, the two levels of control allow a 120-fold range of regulation of the L. lactis operon by histidine.

5' Untranslated Regions↗

PubMed2001

Genetic and structural organization of the aminophenol catabolic operon and its implication for evolutionary process.

The aminophenol (AP) catabolic operon in Pseudomonas putida HS12 mineralizing nitrobenzene was found to contain all the enzymes responsible for the conversion of AP to pyruvate and acetyl coenzyme A via extradiol meta cleavage of 2-aminophenol. The sequence and functional analyses of the corresponding genes of the operon revealed that the AP catabolic operon consists of one regulatory gene, nbzR, and the following nine structural genes, nbzJCaCbDGFEIH, which encode catabolic enzymes. The NbzR protein, which is divergently transcribed with respect to the structural genes, possesses a leucine zipper motif and a MarR homologous domain. It was also found that NbzR functions as a repressor for the AP catabolic operon through binding to the promoter region of the gene cluster in its dimeric form. A comparative study of the AP catabolic operon with other meta cleavage operons led us to suggest that the regulatory unit (nbzR) was derived from the MarR family and that the structural unit (nbzJCaCbDGFEIH) has evolved from the ancestral meta cleavage gene cluster. It is also proposed that these two functional units assembled through a modular type gene transfer and then have evolved divergently to acquire specialized substrate specificities (NbzCaCb and NbzD) and catalytic function (NbzE), resulting in the creation of the AP catabolic operon. The evolutionary process of the AP operon suggests how bacteria have efficiently acquired genetic diversity and expanded their metabolic capabilities by modular type gene transfer.

Amino Acid Sequence↗

PubMed2001

Involvement of a CbbR homolog in low CO2-induced activation of the bicarbonate transporter operon in cyanobacteria.

The cmpABCD operon of Synechococcus sp. strain PCC 7942, encoding a high-affinity bicarbonate transporter, is transcribed only under CO2-limited conditions. In Synechocystis sp. strain PCC 6803, the slr0040, slr0041, slr0043, and slr0044 genes, forming an operon with a putative porin gene (slr0042), were identified as the cmpA, cmpB, cmpC, and cmpD genes, respectively, on the basis of their strong similarities to the corresponding Synechococcus cmp genes and their induction under low CO2 conditions. Immediately upstream of and transcribed divergently from the Synechocystis cmp operon is a gene (sll0030) encoding a homolog of CbbR, a LysR family transcriptional regulator of the CO2 fixation operons of chemoautotrophic and purple photosynthetic bacteria. Inactivation of sll0030, but not of another closely related cbbR homolog (sll1594), abolished low CO2 induction of cmp operon expression. Gel retardation assays showed specific binding of the Sll0030 protein to the sll0030-cmpA intergenic region, suggesting that the protein activates transcription of the cmp operon by interacting with its regulatory region. A cbbR homolog similar to sll0030 and sll1594 was cloned from Synechococcus sp. strain PCC 7942 and shown to be involved in the low CO2-induced activation of the cmp operon. We hence designated the Synechocystis sll0030 gene and the Synechococcus cbbR homolog cmpR. In the mutants of the cbbR homologs, upregulation of ribulose-1,5-bisphosphate carboxylase/oxygenase operon expression by CO2 limitation was either unaffected (strain PCC 6803) or enhanced (strain PCC 7942), suggesting existence of other low CO2-responsive transcriptional regulator(s) in cyanobacteria.

ATP-Binding Cassette Transporters↗

PubMed2002

Characterization of an rRNA operon (rrnB) of Mycobacterium fortuitum and other mycobacterial species: implications for the classification of mycobacteria.

Mycobacteria are thought to have either one or two rRNA operons per genome. All mycobacteria investigated to date have an operon, designated rrnA, located downstream from the murA gene. We report that Mycobacteriun fortuitum has a second rrn operon, designated rrnB, which is located downstream from the tyrS gene; tyrS is very close to the 3' end of a gene (3-mag) coding for 3-methylpurine-DNA-glycosylase. The second rrn operon of Mycobacterium smegmatis was shown to have a similar organization, namely, 5' 3-mag-tyrS-rrnB 3'. The rrnB operon of M. fortuitum was found to have a single dedicated promoter. During exponential growth in a rich medium, the rrnB and rrnA operons were the major and minor contributors, respectively, to pre-rRNA synthesis. Genomic DNA was isolated from eight other fast-growing mycobacterial species. Samples were investigated by Southern blot analysis using probes for murA, tyrS, and 16S rRNA sequences. The results revealed that both rrnA and rrnB operons were present in each species. The results form the basis for a proposed new scheme for the classification of mycobacteria. The approach, which is phylogenetic in concept, is based on particular properties of the rrn operons of a cell, namely, the number per genome and a feature of 16S rRNA gene sequences.

Base Sequence↗

PubMed1983

Cysteine starvation, isoleucyl-tRNAIle, and the regulation of the ilvGEDA operon of Escherichia coli.

The involvement of undermodified tRNA in the regulation of the ilvGEDA operon has been investigated using Escherichia coli C6, a relA-, Cys-, Met- mutant. This strain accumulates thionucleotide-deficient or methyl-deficient tRNA when starved for cysteine or methionine, respectively. The levels of threonine deaminase, the ilvA gene product, and transaminase B, the ilvE gene product, were both lower in cysteine-starved cells, as compared with either growing or methionine-starved cultures. When cysteine was added to cysteine-starved cells, growth ensued promptly and both enzyme activities returned to control levels. Treatment of recovering cultures with valine limited growth by isoleucine limitation, but did not cause a derepression of the ilvGEDA operon. Valine treatment of nonstarved or methionine-starved cells led to the expected increase in threonine deaminase and transaminase B activities. Cysteine-starved cells slowly regained the ability to derepress the operon after 3 h of recovery in complete medium. In contrast, the induction of the lac operon was normal in cysteine-starved cultures, even in the presence of valine. The loss of derepressibility of the ilvGEDA operon was correlated with the presence of a kinetically and chromatographically altered tRNAIle in cysteine-starved cells. No changes in tRNAIle were observed after methionine starvation. Using the periodate method, we found that the charging of tRNAIle increased from the normal level of 60 to 80% or greater after starvation for cysteine. Under conditions where the ilvGEDA operon was fully derepressed in nonstarved cells, the charging of tRNAIle fell to 27%. Unexpectedly, nearly identical results were obtained with cysteine-starved cells after an identical derepression test. These results suggest that factors other than the aminoacylation state of tRNAIle may be important in the regulation of this operon. In particular, modifications to tRNA which involve cysteine may be necessary for controlling the expression of the ilvGEDA operon in E. coli.

Amino Acids↗

PubMed1998

Sequencing and characterization of the xyl operon of a gram-positive bacterium, Tetragenococcus halophila.

The xyl operon of a gram-positive bacterium, Tetragenococcus halophila (previously called Pediococcus halophilus), was cloned and sequenced. The DNA was about 7.7 kb long and contained genes for a ribose binding protein and part of a ribose transporter, xylR (a putative regulatory gene), and the xyl operon, along with its regulatory region and transcription termination signal, in this order. The DNA was AT rich, the GC content being 35.8%, consistent with the GC content of this gram-positive bacterium. The xyl operon consisted of three genes, xylA, encoding a xylose isomerase, xylB, encoding a xylulose kinase, and xylE, encoding a xylose transporter, with predicted molecular weights of 49,400, 56,400, and 51,600, respectively. The deduced amino acid sequences of the XylR, XylA, XylB, and XylE proteins were similar to those of the corresponding proteins in other gram-positive and -negative bacteria, the similarities being 37 to 64%. Each polypeptide of XylB and XylE was expressed functionally in Escherichia coli. XylE transported D-xylose in a sodium ion-dependent manner, suggesting that it is the first described xylose/Na+ symporter. The XylR protein contained a consensus sequence for binding catabolites of glucose, such as glucose-6-phosphate, which has been discovered in glucose and fructose kinases in bacteria. Correspondingly, the regulatory region of this operon contained a putative binding site of XylR with a palindromic structure. Furthermore, it contained a consensus sequence, CRE (catabolite-responsive element), for binding CcpA (catabolite control protein A). We speculate that the transcriptional regulation of this operon resembles the regulation of catabolite-repressible operons such as the amy, lev, xyl, and gnt operons in various gram-positive bacteria. We discuss the significance of the regulation of gene expression of this operon in T. halophila.

Amino Acid Sequence↗

PubMed1969

Relationships between the regulation of the lactose and galactose operons of Escherichia coli.

A group of structurally related compounds, including galactose, fucose, and a number of galactosides, are regulatory effectors for both the lac and gal operons of Escherichia coli. Although a common set of effectors exists, each operon appears to be regulated independently of the other. Experiments with various regulatory mutants have shown, first, that the presence of the proteins of one operon is without effect on the regulation of the other and, second, that the influence an effector has on one operon is independent of the presence or the functional state of the regulatory genes of the other operon. It is unlikely, therefore, that the two operons share a common regulatory macromolecule. Both gal R(-) and gal o(c) regulatory mutants are equally resistant to repression by glucose and galactosides. It has been possible to show, in the gal operon, that induction and repression are competitive processes. For this operon, the differential rate of enzyme synthesis is set by the relative intracellular concentrations of inducer (fucose) and repressor (isopropylthiogalactoside).

Enzyme Induction↗

PubMed1986

opp-lac Operon fusions and transcriptional regulation of the Escherichia coli trp-linked oligopeptide permease.

The transcriptional regulation of the Escherichia coli trp-linked opp operon that encodes the oligopeptide permease was investigated by using lambda plac Mu51-generated lac operon fusions. Synthesis of beta-galactosidase by strains harboring oppA-lac, oppB-lac, and oppD-lac fusions occurred at a basal level when the fusion-containing strains were grown in minimal medium. The addition of L-leucine or L-alanine to exponentially growing, aerobic cultures or shifting the aerobic fusion-containing strains to anaerobic growth medium increased the synthesis of beta-galactosidase from all opp-lac fusions. When transcription of the opp operon was induced by L-leucine, the differential rate of beta-galactosidase synthesis from each opp-lac fusion increased 8- to 10-fold; this increased rate of lacZ expression from the opp-lac fusions resulted in a 5- to 6-fold increase in total beta-galactosidase activity after maximum expression was achieved. Importantly, when F'123 derivatives harboring independently isolated E. coli opp-lac operon fusions were introduced into E. coli and Salmonella typhimurium, the data clearly demonstrated that the E. coli opp operon was expressed identically and responded to the same transcriptional regulatory signals in both E. coli and S. typhimurium. A comparison of beta-galactosidase synthesis by E. coli strains harboring an opp-lac operon fusion and either an oppE+ locus or an oppE mutation demonstrated that the reduction in peptide transport produced by the oppE mutation does not result from a decrease in the level of opp operon transcription.

Alanine↗

PubMed1993

Similar organization of the nusA-infB operon in Bacillus subtilis and Escherichia coli.

We reported previously the cloning and sequence of the Bacillus subtilis infB gene which encodes the essential IF2 factor required for initiation of translation (K. Shazand, J. Tucker, R. Chiang, K. Stansmore, H. U. Sperling-Petersen, M. Grunberg-Manago, J. C. Rabinowitz, and T. Leighton, J. Bacteriol. 172:2675-2687, 1990). The location of the 5' border of the infB operon was investigated by using integrative plasmids carrying various DNA fragments from the region upstream of the infB gene. The lethal effect of disruption of the infB transcriptional unit could be suppressed when the integrated plasmid introduced the spac promoter upstream of the infB operon and transformants were selected in conditions of induction of spac expression. Such an integrated plasmid was used as a starting point to clone the promoter of the infB operon. Primer extension mapping suggests that a single sigma A-type promoter controls transcription of the infB operon. The sequence of a 5,760-bp region encompassing the infB gene was determined. The infB operon is located immediately downstream of the polC gene and comprises seven open reading frames, four of which appear to be the homologs of genes present in the same order in the Escherichia coli infB operon, including nusA. The striking similarity between the E. coli and B. subtilis infB operons suggests that the function of each gene pair is conserved and that the B. subtilis NusA homolog, which is 124 residues shorter than its E. coli counterpart, could play a role similar to its role in E. coli.

Amino Acid Sequence↗

PubMed1996

Loss of overproduction of polypeptide release factor 3 influences expression of the tryptophanase operon of Escherichia coli.

Expression of the tryptophanase (tna) operon of Escherichia coli is regulated by catabolite repression and by tryptophan-induced inhibition of Rho-mediated transcription termination. Previous studies indicated that tryptophan induction might involve leader peptide inhibition of ribosome release at the stop codon of tnaC, the coding region for the operon-specified leader peptide. In this study we examined tna operon expression in strains in which the structural gene for protein release factor 3, prfC, is either disrupted or overexpressed. We find that prfC inactivation leads to a two- to threefold increase in basal expression of the tna operon and a slight increase in induced expression. Overexpression of prfC has the opposite effect and reduces both basal and induced expression. These effects occur in the presence of glucose and cyclic AMP, and thus Rho-dependent termination rather than catabolite repression appears to be the event influenced by the prfC alterations. prfC inactivation also leads to an increase in basal tna operon expression in various rho and rpoB mutants but not in a particular rho mutant in which the basal level of expression is very high. The effect of prfC inactivation was examined in a variety of mutants with alterations in the tna leader region. Our results suggest that translation of tnaC is essential for the prfC effect. The tryptophan residue specified by tnaC codon 12, which is essential for induction, when replaced by another amino) acid, allows the prfC effect. Introducing UAG or UAA stop codons rather than the normal tnaC UGA stop codon, in a strain with an inactive prfC gene, also leads to an increase in the basal level of expression. Addition of the drug bicyclomycin increases basal operon expression of all mutant strains except a strain with a tnaC'-'lacZ fusion. Expression in the latter strain is unaffected by prfC alterations. Our findings are consistent with the interpretation that ribosome release at the tnaC stop codon can influence tna operon expression.

Bacterial Proteins↗

PubMed1990

The role of FIS in trans activation of stable RNA operons of E. coli.

The thrU(tufB) operon of Escherichia coli is endowed with a cis-acting region upstream of the promoter, designated UAS for Upstream Activator Sequence. A protein fraction has been isolated that binds specifically to DNA fragments of the UAS, thus forming three protein-DNA complexes corresponding to three binding sites on the UAS. It stimulates in vitro transcription of the operon by facilitating the binding of the RNA polymerase to the promoter. All three protein-DNA complexes contain one and the same protein. Dissociation constants for the three complexes have been determined, the lowest being in the sub-nanomolar range. The protein also binds to the UAS of the tyrT operon and to the UAS upstream of the P1 promoter of the rrnB operon, suggesting that transcription of the three operons, if not of more stable RNA operons, is activated by a common trans activator. We demonstrate that the E.coli protein FIS (Factor for Inversion Stimulation) also binds to the UAS of the thrU(tufB) operon forming three protein-DNA complexes. A burst of UAS- and FIS-dependent promoter activity is observed after reinitiation of growth of stationary cultures in fresh medium.

Carrier Proteins↗