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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Klebsiella pneumoniae NifL antagonizes the action of the transcriptional activator NifA in the presence of molecular oxygen or combined nitrogen. To determine what cofactors might be involved in the oxygen sensing mechanism, we purified and analyzed fusion proteins made between the Escherichia coli maltose binding protein, MalE, and NifL. NifL synthesized and purified under strictly anaerobic conditions did not contain significant amounts of iron or acid-labile sulfur indicating the absence of an oxygen sensing iron-sulfur cluster. However, NifL protein purified in its inhibitory form contained 0.3 +/- 0.01 mol FAD and less than 0.01 mol FMN per mol NifL suggesting the presence of FAD as a cofactor. Characterization of NifL synthesized in the absence of oxygen and combined nitrogen showed that the non-inhibitory form of NifL also contained FAD (0.54 mol FAD per mol NifL). Using fusions between MalE and different portions of NifL we localized the binding site of FAD to the N-terminal domain of NifL. These results and our previous observation that the C-terminal domain of NifL is sufficient to inhibit NifA activity indicate that the N-terminally bound FAD is not directly required for the inhibitory activity of NifL. This observation is supported by the finding that purified apoprotein of NifL was still able to inhibit transcriptional activation by NifA in vitro.
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PMID:NifL of Klebsiella pneumoniae carries an N-terminally bound FAD cofactor, which is not directly required for the inhibitory function of NifL. 943 14

During development of root nodules, Rhizobium bacteria differentiate inside the invaded plant cells into N2-fixing bacteroids. Terminally differentiated bacteroids are unable to grow using the ammonia (NH3) produced therein by the nitrogenase complex. Therefore, the nitrogen assimilation activities of bacteroids, including the ammonium (NH4+) uptake activity, are expected to be repressed during symbiosis. By sequence homology the R. etli amtB (ammonium transport) gene was cloned and sequenced. As previously shown for its counterpart in other organisms, the R. etli amtB gene product mediates the transport of NH4+. The amtB gene is cotranscribed with the glnK gene (coding for a PII-like protein) from a nitrogen-regulated sigma 54-dependent promoter, which requires the transcriptional activator NtrC. Expression of the glnKamtB operon was found to be activated under nitrogen-limiting, free-living conditions, but down-regulated just when bacteria are released from the infection threads and before transcription of the nitrogenase genes. Our data suggest that the uncoupling between N2-fixation and NH3 assimilation observed in symbiosomes is generated by a transcriptional regulatory mechanism(s) beginning with the inactivation of NtrC in younger bacteroids.
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PMID:The Rhizobium etli amtB gene coding for an NH4+ transporter is down-regulated early during bacteroid differentiation. 948 94

IME1 encodes a transcriptional activator required for the transcription of meiosis-specific genes and initiation of meiosis in Saccharomyces cerevisiae. The transcription of IME1 is repressed in the presence of glucose, and a low basal level of IME1 RNA is observed in vegetative cultures with acetate as the sole carbon source. Upon nitrogen depletion a transient induction in the transcription of IME1 is observed in MATa/MATalpha diploids but not in MAT-insufficient strains. In this study we demonstrate that the transcription of IME1 is controlled by an extremely unusual large 5' region, over 2,100 bp long. This area is divided into four different upstream controlling sequences (UCS). UCS2 promotes the transcription of IME1 in the presence of a nonfermentable carbon source. UCS2 is flanked by three negative regions: UCS1, which exhibits URS activity in the presence of nitrogen, and UCS3 and UCS4, which repress the activity of UCS2 in MAT-insufficient cells. UCS2 consists of alternate positive and negative elements: three distinct constitutive URS elements that prevent the function of any upstream activating sequence (UAS) under all growth conditions, a constitutive UAS element that promotes expression under all growth conditions, a UAS element that is active only in vegetative media, and two discrete elements that function as UASs in the presence of acetate. Sequence analysis of IME1 revealed the presence of two almost identical 30- to 32-bp repeats. Surprisingly, one repeat, IREd, exhibits constitutive URS activity, whereas the other repeat, IREu, serves as a carbon-source-regulated UAS element. The RAS-cyclic AMP-dependent protein kinase cAPK pathway prevents the UAS activity of IREu in the presence of glucose as the sole carbon source, while the transcriptional activators Msn2p and Msn4p promote the UAS activity of this repeat in the presence of acetate. We suggest that the use of multiple negative and positive elements is essential to restrict transcription to the appropriate conditions and that the combinatorial effect of the entire region leads to the regulated transcription of IME1.
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PMID:Multiple and distinct activation and repression sequences mediate the regulated transcription of IME1, a transcriptional activator of meiosis-specific genes in Saccharomyces cerevisiae. 952 70

NtcA is a transcriptional activator involved in global nitrogen control in cyanobacteria. In the absence of ammonium it regulates the transcription of a series of genes encoding proteins required for the uptake and assimilation of alternative nitrogen sources (I. Luque, E. Flores, and A. Herrero, EMBO J. 13:2862-2869, 1994). ntcA, present in a single copy in the marine Synechococcus sp. strain WH 7803, was cloned and sequenced. The putative amino acid sequence shows a high degree of identity to NtcA from freshwater cyanobacteria in two functional domains. The expression of ntcA was negatively regulated by ammonium from a putative transcription start point located downstream of an NtcA consensus recognition sequence. Addition of either rifampin or ammonium led to a rapid decline in ntcA transcript levels with half-lives of less than 2 min in both cases. Nitrate-grown cells showed high ntcA transcript levels, as well as the capacity for active nitrite uptake. However, ammonium-grown cells showed low levels of the ntcA transcript and did not utilize nitrite. The addition of ammonium to nitrite uptake-active cells resulted in a gradual decline in the rate of uptake over a 24-h period. Active nitrite uptake was not induced in cells transferred to medium lacking a nitrogen source despite evidence of elevated expression of ntcA, indicating that ntcA expression is not sufficient for uptake capacity to develop. Nitrate and nitrite addition led to the development of nitrite uptake, whereas the addition of leucine did not. Furthermore, nitrite addition triggered the de novo protein synthesis required for uptake capacity to develop. These data suggest that nitrite and nitrate act as specific inducers for the synthesis of proteins required for nitrite uptake.
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PMID:Regulation of ntcA expression and nitrite uptake in the marine Synechococcus sp. strain WH 7803. 953 88

Azotobacter vinelandii NIFL is a nitrogen fixation-specific regulatory flavoprotein that modulates the activity of the transcriptional activator NIFA in response to oxygen and fixed nitrogen in vivo. NIFL is also responsive to ADP in vitro. Limited proteolysis of NIFL indicates that it comprises a relatively stable N-terminal domain and a C-terminal domain that is protected from trypsin digestion in the presence of adenosine nucleotides. ATP protects the protein from cleavage in the vicinity of potential nucleotide-binding sites in the C-terminus, whereas ADP protects the entire C-terminal domain. NIFL has an apparent Kd of 130 microM for ATP and 16 microM for ADP. The purified N-terminal domain has an identical UV/visible absorption spectrum to the wild-type protein and is reduced by sodium dithionite, demonstrating that it is a flavin-binding domain. The isolated N-terminal domain does not inhibit NIFA activity. A subdomain fragment containing 160 residues of the C-terminal region, including the nucleotide-binding sites, is also not competent to inhibit NIFA. Removal of the first 146 residues of NIFL, which includes a conserved S-motif (PAS-like domain), found in a large family of sensory proteins from eubacteria, archea and eukarya eliminates the redox response. However, this truncated protein remains competent to inhibit NIFA activity in response to ADP in vitro and to the level of fixed nitrogen in vivo. The redox and nitrogen-sensing functions of A. vinelandii NIFL are therefore separable and are discrete functions of the protein.
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PMID:The redox- and fixed nitrogen-responsive regulatory protein NIFL from Azotobacter vinelandii comprises discrete flavin and nucleotide-binding domains. 959 6

Transcriptional control of the nitrogen fixation (nif) genes in response to oxygen in Azotobacter vinelandii is mediated by nitrogen fixation regulatory protein L (NifL), a regulatory flavoprotein that modulates the activity of the transcriptional activator nitrogen fixation regulatory protein A (NifA). CD spectra of purified NifL indicate that FAD is bound to NifL in an asymmetric environment and the protein is predominantly alpha-helical. The redox potential of NifL is -226 mV at pH 8 as determined by the enzymic reduction of NifL by xanthine oxidase/xanthine in the presence of appropriate mediators. The reduction of NifL by xanthine oxidase prevented NifL from acting as an inhibitor of NifA. In the absence of electron mediators NifL could also be reduced by Escherichia coli flavohaemoprotein (Hmp) with NADH as reductant. Hmp contains a globin-like domain with haem B as prosthetic group and an FAD-containing oxidoreductase module. The carboxyferrohaem form of Hmp was competent to reduce NifL, suggesting that electron donation to NifL originates from the flavin in Hmp rather than by direct electron transfer from the haem. Spinach ferredoxin:NAD(P) oxidoreductase, which adopts a folding similar to the FAD- and NAD-binding domains of Hmp, also reduced NifL with NADH as reductant. Re-oxidation of NifL occurs rapidly in the presence of air, raising the possibility that NifL might sense intracellular oxygen. We propose a physiological redox cycle in which the oxidation of NifL by oxygen and hence the activation of its inhibitory properties occurs rapidly, in contrast with the switch from the active to the reduced form of NifL, which occurs more slowly.
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PMID:Electron donation to the flavoprotein NifL, a redox-sensing transcriptional regulator. 960 Oct 70

The roles of the nitrogen fixation regulatory proteins NifA, FixK1, and FixK2 in the symbiotic regulation of hydrogenase structural gene expression in Bradyrhizobium japonicum have been investigated. Bacteroids from FixJ and FixK2 mutants have little or no hydrogenase activity, and extracts from these mutant bacteroids contain no hydrogenase protein. Bacteroids from a FixK1 mutant exhibit wild-type levels of hydrogenase activity. In beta-galactosidase transcriptional assays with NifA and FixK2 expression plasmids, the FixK2 protein induces transcription from the hup promoter to levels similar to those induced by HoxA, the transcriptional activator of free-living hydrogenase expression. The NifA protein does not activate transcription at the hydrogenase promoter. Therefore, FixK2 is involved in the transcriptional activation of symbiotic hydrogenase expression. By using beta-galactosidase transcriptional fusion constructs containing successive truncations of the hup promoter, the region of the hup promoter required for regulation by FixK2 was determined to be between 29 and 44 bp upstream of the transcription start site.
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PMID:The FixK2 protein is involved in regulation of symbiotic hydrogenase expression in Bradyrhizobium japonicum. 962 Sep 82

The prnA gene codes for a transcriptional activator that mediates proline induction of four other genes involved in proline utilization as a nitrogen and/or carbon source in Aspergillus nidulans. In this paper, we present the genomic and cDNA sequence and the transcript map of prnA. The PrnA protein belongs to the Zn binuclear cluster family of transcriptional activators. The gene shows a striking intron-exon organization, with the putative nuclear localization sequence and the Zn cluster domain in discrete exons. Although the protein sequence presents some interesting similarities with the isofunctional protein of Saccharomyces cerevisiae Put3p, a higher degree of similarity is found with a functionally unrelated protein Thi1 of Schizosaccharomyces pombe. A number of mutations mapping in the prnA gene were sequenced. This comprises a deletion that results in an almost complete loss of the prnA-specific mRNA, a mutation in the putative nuclear localization signal, a proline to leucine mutation in the second loop of the zinc cluster and a cold-sensitive mutation in the so-called 'central region'. Other complete or partial loss of function mutations map in regions of unknown function. We establish that the transcription of the gene is neither self-regulated nor significantly affected by carbon and/or nitrogen metabolite repression.
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PMID:Sequence, exon-intron organization, transcription and mutational analysis of prnA, the gene encoding the transcriptional activator of the prn gene cluster in Aspergillus nidulans. 962 60

Many nitrogen fixation-associated genes in the soybean symbiont Bradyrhizobium japonicum are regulated by the transcriptional activator NifA, whose activity is inhibited by aerobiosis. NifA is encoded in the fixR-nifA operon, which is expressed at a low level under aerobic conditions and induced approximately fivefold under low-oxygen tension. This induction depends on a -24/-12-type promoter (fixRp1) that is recognized by the sigma54 RNA polymerase and activated by NifA. Low-level aerobic expression and part of the anaerobic expression originates from a second promoter (fixRp2) that overlaps with fixRp1 and depends on an upstream DNA region (UAS) located around position -68 (H. Barrios, H. M. Fischer, H. Hennecke, and E. Morett, J. Bacteriol. 177:1760-1765, 1995). A protein binding to the UAS was previously postulated to act as an activator. This protein has now been purified, and the corresponding gene (regR) has been cloned. On the basis of the predicted amino acid sequence, RegR belongs to the family of response regulators of two-component regulatory systems. We identified upstream of the regR gene an additional gene (regS) encoding a putative sensor kinase. A regR mutant was constructed in which neither a specific UAS-binding activity nor fixRp2-dependent transcript formation and fixR'-'lacZ expression was detected in aerobically grown cells. Anaerobic fixR'-'lacZ expression was also decreased in regR mutants to about 10% of the level observed in the wild type. Similarly, regR mutants showed only about 2% residual nitrogen fixation activity, but unlike nodules induced by nifA mutants, the morphology of those nodules was normal, displaying no signs of necrosis. While regR mutants grew only slightly slower in free-living, aerobic conditions, they displayed a strong growth defect under anaerobic conditions. The phenotypic properties of regS mutants differed only marginally, if at all, from those of the wild type, suggesting the existence of a compensating sensor activity in these strains. The newly identified RegR protein may be regarded as a master regulator in the NifA-dependent network controlling nif and fix gene expression in B. japonicum.
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PMID:Expression of the fixR-nifA operon in Bradyrhizobium japonicum depends on a new response regulator, RegR. 968 82

Two structurally similar but functionally distinct PII-like proteins, PII and GlnK, regulate nitrogen assimilation in Escherichia coli. Studies with cells indicated that both PII (the glnB product) and GlnK (the glnK product) acted through the kinase/phosphatase NRII [NtrB, the glnL (ntrB) product] to reduce transcription initiation from Ntr promoters, apparently by regulating the phosphorylation state of the transcriptional activator NRI-P (NtrC-P, the phosphorylated form of the glnG (ntrC) product). Both GlnK and PII also acted through adenylyltransferase (ATase, the glnE product) to regulate the adenylylation state of glutamine synthetase (GS). The activity of both GlnK and PII was regulated by the signal-transducing uridylyltransferase/uridylyl-removing enzyme (UTase/UR, glnD product). Our experiments indicate that either PII or GlnK could effectively regulate ATase, but that PII was required for the efficient regulation of NRII required to prevent expression of glnA, which encodes GS. Yet, GlnK also participated in regulation of NRII. Although cells that lack either PII or GlnK grew well, cells lacking both of these proteins were defective for growth on nitrogen-rich minimal media. This defect was alleviated by the loss of NRII, and was apparently due to unregulated expression of the Ntr regulon. Also, mutations in glnK, designated glnK*, were obtained as suppressors of the Ntr- phenotype of a double mutant lacking PII and the UTase/UR. These suppressors appeared to reduce, but not eliminate, the ability of GlnK to prevent Ntr gene expression by acting through NRII. We hypothesize that one role of GlnK is to regulate the expression of the level of NRI-P during conditions of severe nitrogen starvation, and by so doing to contribute to the regulation of certain Ntr genes.
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PMID:Role of the GlnK signal transduction protein in the regulation of nitrogen assimilation in Escherichia coli. 972 Aug 63


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