Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Symbiotic nitrogen fixation is accompanied by a shift of Rhizobium nitrogen metabolism from ammonium assimilation to ammonium export, which probably involves genetic or metabolic regulation of glutamine synthetase activity. In free-living Rhizobium meliloti glutamine synthetase I (GSI) is regulated post-translationally by reversible adenylylation in response to ammonium addition. Moreover, full expression of the GSI gene glnA requires the transcriptional activator, NtrC. A glnA1 mutant synthesizing a non-adenylylatable GSI produces normal nitrogen-fixing nodules on alfalfa: GSI adenylylation is dispensable for symbiotic nitrogen fixation. This is rationalized by the observation that less GS protein is present in R. meliloti bacteroids than in free-living bacterial cells.
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PMID:Symbiotic nitrogen fixation does not require adenylylation of glutamine synthetase I in Rhizobium meliloti. 893 24

The production of pectin lyase (Pnl) in Erwinia carotovora ssp. carotovora strain 71 is induced by DNA-damaging agents such as mitomycin C (MC). This induction requires functions of recA, rdgA and rdgB genes. Based upon sequence homology, rdgA was predicted to encode a repressor and rdgB was presumed to specify a transcriptional activator. To elucidate the function of rdgA, the gene has been over-expressed in Escherichia coli, and the 30 kDa product purified by ammonium-sulphate precipitation, heparin-agarose chromatography and gel filtration. The results of gel mobility-shift and DNase I protection assays revealed that purified RdgA specifically binds the rdgA operator sequence located between the -10 and -35 boxes. The expression of a rdgA-lacZ gene fusion in E. coli MC4100 is suppressed upon overproduction of RdgA from a Ptac-rdgA construct induced by isopropyl-beta-D-thiogalactopyranoside (IPTG). However, the suppression of rdgA-tacZ expression is relieved by MC in the RecA+ E. coli strain MC4100, but not in its RecA- derivative, MC4160. An immunoblot analysis revealed RecA-dependent in vivo cleavage of the 30 kDa RdgA protein upon MC treatment. These results demonstrate that the transcription of rdgA is autoregulated, and strongly support the idea that proteolytic activity of RecA* is responsible for the derepression of rdgA expression.
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PMID:RecA relieves negative autoregulation of rdgA, which specifies a component of the RecA-Rdg regulatory circuit controlling pectin lyase production in Erwinia carotovora ssp. carotovora. 897 12

In cyanobacteria, ammonium represses expression of proteins involved in nitrogen fixation and assimilation. The global nitrogen regulator gene ntcA encodes a DNA-binding protein, NtcA, that is a transcriptional activator of genes subject to nitrogen control. We report the cloning and sequencing of the ntcA gene from a nitrogen-fixing unicellular cyanobacterium, Cyanothece sp. strain BH68K. The gene comprises 678 nucleotides, and the deduced NtcA protein contains 226 amino acids with a predicted molecular weight of 25,026. In addition, ntcA mRNA levels were measured in cells grown under different nitrogen regimes. Under nitrogen-fixing conditions, ntcA transcripts were weakly expressed. Furthermore, ntcA expression was diminished or inversely proportional to nifHDK expression. Conversely, ntcA expression increased in nitrate-grown cells, and a concentration-dependent increase was seen in ammonium-grown cells up to 1 mM NH4Cl. These results indicate that ntcA is involved more in nitrogen assimilation than in nitrogen fixation and also imply that the rhythmic expression of ntcA and nifHDK transcription may be under the control of a circadian clock.
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PMID:Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K. 920 62

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

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

In Herbaspirillum seropedicae, an endophytic diazotroph, nif gene expression is under the control of the transcriptional activator NifA. We have over-expressed and purified a protein containing the central and C-terminal domains of the H. seropedicae NifA protein, N-truncated NifA, fused to a His-Tag sequence. This fusion protein was found to be partially soluble and was purified by affinity chromatography. Band shift and footprinting assays showed that the N-truncated NifA protein was able to bind specifically to the H. seropedicae nifB promoter region. In vivo analysis showed that this protein activated the nifH promoter of Klebsiella pneumoniae in Escherichia coli only in the absence of oxygen and this activation was not negatively controlled by ammonium ions.
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PMID:Expression and functional analysis of an N-truncated NifA protein of Herbaspirillum seropedicae. 1021 62

In Klebsiella pneumoniae, NifL modulates the activity of the transcriptional activator NifA in response to combined nitrogen or external molecular oxygen. We recently showed that K. pneumoniae NifL is a flavoprotein which apparently senses oxygen through a redox-sensitive, conformational change. In order to study whether the nitrogen signal might be transmitted to NifA through a stable modification of NifL we characterized the redox properties of NifL synthesized in Escherichia coli in the presence of different nitrogen sources. FAD analyses showed that purified NifL carried FAD as cofactor independent of nitrogen and oxygen availability. The redox potential of NifL synthesized in the presence of ammonium was -277+/-5 mV at pH 8.0 and 25 degrees C, as determined by reduction with dithionite or with enzymatic reduction by xanthine oxidase in the presence of methyl viologen as redox mediator. When synthesized under nitrogen-limiting conditions, NifL showed a redox potential of -274+/-6 mV at pH 8.0 and 25 degrees C. Fully reduced NifL fractions, synthesized under either condition listed above, reoxidized rapidly in the presence of molecular oxygen. These results indicate that for NifL synthesized in E. coli, the redox potential of the NifL-bound FAD is not influenced by the nitrogen source. The two NifL fractions differed, however, in that a non-flavin specific absorbance at 420 nm was found only in NifL synthesized in the presence of ammonium.
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PMID:NifL of Klebsiella pneumoniae: redox characterization in relation to the nitrogen source. 1035 Jun 21

The catabolite control protein CcpA is a central regulator in low-G+C-content gram-positive bacteria. It confers carbon catabolite repression to numerous genes required for carbon utilization. It also operates as a transcriptional activator of genes involved in diverse phenomena, such as glycolysis and ammonium fixation. We have cloned the ccpA region of Lactobacillus pentosus. ccpA encodes a protein of 336 amino acids exhibiting similarity to CcpA proteins of other bacteria and to proteins of the LacI/GalR family of transcriptional regulators. Upstream of ccpA was found an open reading frame with similarity to the pepQ gene, encoding a prolidase. Primer extension experiments revealed two start sites of transcription for ccpA. In wild-type cells grown on glucose, mRNA synthesis occurred only from the promoter proximal to ccpA. In a ccpA mutant strain, both promoters were used, with increased transcription from the distant promoter, which overlaps a presumptive CcpA binding site called cre (for catabolite responsive element). This suggests that expression of ccpA is autoregulated. Determination of the expression levels of CcpA in cells grown on repressing and nonrepressing carbon sources revealed that the amounts of CcpA produced did not change significantly, leading to the conclusion that the arrangement of two promoters may ensure constant expression of ccpA under various environmental conditions. A comparison of the genetic structures of ccpA regions revealed that lactic acid bacteria possess the gene order pepQ-ccpA-variable while the genetic structure in bacilli and Staphylococcus xylosus is aroA-ccpA-variable-acuC.
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PMID:Carbon catabolite repression in Lactobacillus pentosus: analysis of the ccpA region. 1061 36

Azospirillum represents the best characterized genus of plant growth-promoting rhizobacteria. Other free-living diazotrophs repeatedly detected in association with plant roots, include Acetobacter diazotrophicus, Herbaspirillum seropedicae, Azoarcus spp. and Azotobacter. Four aspects of the Azospirillum-plant root interaction are highlighted: natural habitat, plant root interaction, nitrogen fixation and biosynthesis of plant growth hormones. Each of these aspects is dealt with in a comparative way. Azospirilla are predominantly surface-colonizing bacteria, whereas A. diazotrophicus, H. seropedicae and Azoarcus sp. are endophytic diazotrophs. The attachment of Azospirillum cells to plant roots occurs in two steps. The polar flagellum, of which the flagellin was shown to be a glycoprotein, mediates the adsorption step. An as yet unidentified surface polysaccharide is believed to be essential in the subsequent anchoring phase. In Azoarcus sp. the attachment process is mediated by type IV pili. Nitrogen fixation structural genes (nif) are highly conserved among all nitrogen-fixing bacteria, and in all diazotrophic species of the class of proteobacteria examined, the transcriptional activator NifA is required for expression of other nif genes in response to two major environmental signals (oxygen and fixed N). However, the mechanisms involved in this control can vary in different organisms. In Azospirillum brasilense and H. seropedicae (alpha- and beta-subgroup, respectively), NifA is inactive in conditions of excess nitrogen. Activation of NifA upon removal of fixed N seems to involve, either directly or indirectly, the signal transduction protein P(II). The presence of four conserved cysteine residues in the NifA protein might be an indication that NifA is directly sensitive to oxygen. In Azotobacter vinelandii (gamma-subgroup) nifA is cotranscribed with a second gene nifL. The nifL gene product inactivates NifA in response to high oxygen tension and cellular nitrogen-status. NifL was found to be a redox-sensitive flavoprotein. The relief of NifL inhibition on NifA activity, in response to N-limitation, is suggested to involve a P(II)-like protein. Moreover, nitrogenase activity is regulated according to the intracellular nitrogen and O(2) level. In A. brasilense and Azospirillum lipoferum posttranslational control of nitrogenase, in response to ammonium and anaerobiosis, involves ADP-ribosylation of the nitrogenase iron protein, mediated by the enzymes DraT and DraG. At least three pathways for indole-3-acetic acid (IAA) biosynthesis in A. brasilense exist: two Trp-dependent (the indole-3-pyruvic acid and presumably the indole-3-acetamide pathway) and one Trp-independent pathway. The occurrence of an IAA biosynthetic pathway not using Trp (tryptophan) as precursor is highly unusual in bacteria. Nevertheless, the indole-3-pyruvate decarboxylase encoding ipdC gene is crucial in the overall IAA biosynthesis in Azospirillum. A number of genes essential for Trp production have been isolated in A. brasilense, including trpE(G) which codes for anthranilate synthase, the key enzyme in Trp biosynthesis. The relevance of each of these four aspects for plant growth promotion by Azospirillum is discussed.
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PMID:Azospirillum, a free-living nitrogen-fixing bacterium closely associated with grasses: genetic, biochemical and ecological aspects. 1097 48

The tam A gene of Aspergillus nidulans encodes a 739-amino acid protein with similarity to Uga35p/Dal81p/DurLp of Saccharomyces cerevisiae. It has been proposed that TamA functions as a co-activator of AreA, the major nitrogen regulatory protein in A. nidulans. Because AreA functions as a transcriptional activator under nitrogen-limiting conditions, we investigated whether TamA was also present in the nucleus. We found that a GFP-TamA fusion protein was predominantly localised to the nucleus in the presence and absence of ammonium, and that AreA was not required for this distribution. As the predicted DNA-binding domain of TamA is not essential for function, we have used a number of approaches to further define functionally important regions. We have cloned the tamA gene of A. oryzae and compared its functional and sequence characteristics with those of A. nidulans tamA and S. cerevisiae UGA35/DAL81/DURL. The Aspergillus homologues are highly conserved and functionally interchangeable, whereas the S. cerevisiae gene does not complement a tamA mutant when expressed in A. nidulans. Uga35p/Dal81p/DurLp was also found to be unable to recruit AreA. The sequence changes in a number of tamA mutant alleles were determined, and altered versions of TamA were tested for tamA complementation and interaction with AreA. Changes in most regions of TamA appeared to destroy its function, suggesting that the overall conformation of the protein may be critical for its activity.
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PMID:Functional analysis of TamA, a coactivator of nitrogen-regulated gene expression in Aspergillus nidulans. 1145 83


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