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)

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

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.
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PMID: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. 1020 9

Uptake of nitrate into the cytoplasm is the first but least well understood step of denitrification; no gene has previously been identified to be necessary for this process. Upstream from the structural genes of the membrane-bound nitrate reductase (narGHJI) in Paracoccus pantotrophus there is a fusion of two genes, each homologous to members of the narK family. The single open reading frame is predicted to encode 24 transmembrane helices, comprising two domains, NarK1 and NarK2. Analysis of both the accumulation of intracellular nitrite and electron transport through the nitrate reductase enzyme in narK mutants reveals that NarK1 and NarK2 are both involved in nitrate uptake. Maximal rate of nitrate transport via NarK2 was dependent upon nitrite, indicating that NarK2 encodes a nitrate/nitrite antiporter. The uncouplers S13 and dinitrophenol showed that NarK2 was not dependent on the proton motive force for maximal nitrate transport activity. Nitrate transport via NarK1 was dependent on proton motive force, indicating that it is likely to be a nitrate/proton symporter. Low expression of membrane-bound nitrate reductase in narK mutants was counteracted by azide, which induced nitrate reductase expression only if the transcriptional activator NarR was present.
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PMID:Two domains of a dual-function NarK protein are required for nitrate uptake, the first step of denitrification in Paracoccus pantotrophus. 1196 76

Paracoccus denitrificans PD1222 accumulates short-length polyhydroxyalkanoates, poly(3-hydroxybutyrate), under nitrogen-deficient conditions. Polyhydroxybutyrate metabolism requires the 3-ketoacyl-CoA thiolase PhaA, the acetoacetyl-CoA dehydrogenase/reductase PhaB and the synthase PhaC for polymerization. Additionally, P. denitrificans PD1222 grows aerobically with nitrate as sole nitrogen source. Nitrate assimilation is controlled negatively by ammonium through the two-component NtrBC system. NtrB is a sensor kinase that autophosphorylates a histidine residue under low-nitrogen concentrations and, in turn, transfers a phosphoryl group to an aspartate residue of the response regulator NtrC protein, which acts as a transcriptional activator of the P. denitrificans PD1222 nasABGHC genes. The P. denitrificans PD1222 NtrB mutant was unable to use nitrate efficiently as nitrogen source when compared to the wild-type strain, and it also overproduced poly(3-hydroxybutyrate). Acetyl-CoA concentration in the P. denitrificans PD1222 NtrB mutant strain was higher than in the wild-type strain. The expression of the phaC gene was also increased in the NtrB mutant when compared to the wild-type strain. These results suggest that accumulation of poly(3-hydroxybutyrate) in the NtrB mutant strain of PD1222 responds to the high levels of acetyl-CoA that accumulate in the cytoplasm as consequence of its inability to efficiently use nitrate as nitrogen source.
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PMID:Poly(3-hydroxybutyrate) hyperproduction by a global nitrogen regulator NtrB mutant strain of Paracoccus denitrificans PD1222. 2922 77