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

The phosphorylated FixJ transcriptional activator is key to nitrogen fixation in Sinorhizobium meliloti, switching both the nifA and fixK genes on. Previously no consensus picture emerged concerning the nature of FixJ binding sites. Here we used in vitro DNA selection in order to systematically characterise FixJ binding sequences. This led to the definition of two classes of sites. Class I sites share the CTAAGTAGTTTCCC sequence found in the fixK promoter, whereas class II sites are defined by a GTAMGTAG consensus octamer. Our results indicate that FixJ approximately P binds DNA following two distinct binding modes.
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PMID:Two distinct classes of FixJ binding sites defined by in vitro selection. 1206 34

The role of leucine biosynthesis by Sinorhizobium meliloti in the establishment of nitrogen-fixing symbiosis with alfalfa ( Medicago sativa) was investigated. The leuA gene from S. meliloti, encoding alpha-isopropylmalate synthase, which catalyses the first specific step in the leucine biosynthetic pathway, was characterized. S. melilotiLeuA(-) mutants were Leu auxotrophs and lacked alpha-isopropylmalate synthase activity. In addition, leuA auxotrophs were unable to nodulate alfalfa. Alfalfa roots did not seem to secrete enough leucine to support growth of leucine auxotrophs in the rhizosphere. Thus, this growth limitation probably imposes the inability to initiate symbiosis. However, in addition to the leucine auxotrophy, leuA strains were impaired in activation of nodulation genes by the transcriptional activator NodD1 in response to the plant flavone luteolin. By contrast, nod gene activation by NodD3, which does not involve plant-derived inducers, was unaffected. Our results suggest that a leucine-related metabolic intermediate may be involved in activation of nodulation genes by NodD1 and luteolin. This kind of control could be of relevance as a way to link bacterial physiological status to the response to plant signals and initiation of symbiosis.
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PMID:Involvement of the Sinorhizobium meliloti leuA gene in activation of nodulation genes by NodD1 and luteolin. 1207 Jul 67

The Bacillus subtilis ycnG (gabT) and ycnH (gabD) genes were shown to encode gamma-aminobutyrate (GABA) aminotransferase and succinic semi-aldehyde dehydrogenase, respectively, and to form a GABA-inducible operon. Null mutations in gabT, gabD or the divergently transcribed ycnF (gabR) gene blocked the utilization of GABA as sole nitrogen source. GabR proved to be a transcriptional activator of the gabTD operon and a negative autoregulator. The target of GabR action was localized to an 87 bp region that includes both gabR and gabT promoters. GabR is a member of a novel but widespread family of chimeric bacterial proteins that have apparent DNA-binding and aminotransferase domains. Mutations in conserved residues of the putative aminotransferase domain abolished GabR function as a transcriptional activator, but did not affect its activity as a negative autoregulator.
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PMID:GabR, a member of a novel protein family, regulates the utilization of gamma-aminobutyrate in Bacillus subtilis. 1212 65

Regulated intracellular localization of Gln3, the transcriptional activator responsible for nitrogen catabolite repression (NCR)-sensitive transcription, permits Saccharomyces cerevisiae to utilize good nitrogen sources (e.g. glutamine and ammonia) in preference to poor ones (e.g. proline). During nitrogen starvation or growth in medium containing a poor nitrogen source, Gln3 is nuclear and NCR-sensitive transcription is high. However, when cells are grown in excess nitrogen, Gln3 is localized to the cytoplasm with a concomitant decrease in gene expression. Treating cells with the Tor protein inhibitor, rapamycin, mimics nitrogen starvation. Recently, carbon starvation has been reported to cause nuclear localization of Gln3 and increased NCR-sensitive transcription. Here we show that nuclear localization of Gln3 during carbon starvation derives from its indirect effects on nitrogen metabolism, i.e. Gln3 does not move into the nucleus of carbon-starved cells if glutamine rather than ammonia is provided as the nitrogen source. In addition, these studies have clearly shown Gln3 is not uniformly distributed in the cytoplasm, but rather localizes to punctate or tubular structures. Analysis of these images by deconvolution microscopy suggests that Gln3 is concentrated in or associated with a highly structured system in the cytosol, one that is possibly vesicular in nature. This finding may impact significantly on how we view (i) the mechanism by which Tor regulates the intracellular localization of Gln3 and (ii) how proteins move into and out of the nucleus.
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PMID:Cytoplasmic compartmentation of Gln3 during nitrogen catabolite repression and the mechanism of its nuclear localization during carbon starvation in Saccharomyces cerevisiae. 1214 Feb 87

The nitrogen-regulated genes and operons of the Ntr regulon of Escherichia coli are activated by the enhancer-binding transcriptional activator NRI approximately P (NtrC approximately P). Here, we examined the activation of the glnA, glnK, and nac promoters as cells undergo the transition from growth on ammonia to nitrogen starvation and examined the amplification of NRI during this transition. The results indicate that the concentration of NRI is increased as cells become starved for ammonia, concurrent with the activation of Ntr genes that have less- efficient enhancers than does glnA. A diauxic growth pattern was obtained when E. coli was grown on a low concentration of ammonia in combination with arginine as a nitrogen source, consistent with the hypothesis that Ntr genes other than glnA become activated only upon amplification of the NRI concentration.
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PMID:Activation of the glnA, glnK, and nac promoters as Escherichia coli undergoes the transition from nitrogen excess growth to nitrogen starvation. 1221 22

Pseudomonas aeruginosa PAO1 utilizes proline as the sole source of carbon and nitrogen via a bifunctional enzyme (the putA gene product) that has both proline dehydrogenase (EC 1.5.99.8) and pyrroline 5-carboxylate dehydrogenase (EC 1.5.1.12) activities. We characterized the pruR-putAP loci encoding the proline catabolic system of this strain. In contrast to the putA and putP (encoding proline permease) genes of other gram- negative bacteria, which are located at divergent or separate loci, Northern blotting demonstrated that the two genes form an operon in strain PAO1. While the phylogenetic lineage of the PutP protein of strain PAO1 was related to that of the origin (80% identity to the P. putida counterpart), PutA of PAO1 (PutA(PAO)) was rather distantly related (47% identity) to the P. putida counterpart. Moreover, unlike the PutA proteins of P. putida and enteric bacteria, PutA(PAO) appeared to lack a regulatory function. Upstream of the putAP operon, the divergent PA0781 gene specified a hypothetical outer membrane protein with a molecular weight of 74,202. This gene appeared to be dispensable for proline utilization as indicated by the normal growth of a knockout mutant of PA0781 on medium containing proline. The pruR (proline utilization regulator) gene immediately upstream of PA0781 encoded a transcriptional activator of the AraC/XylS protein family and mediated the proline-responsive expression of putAP. Primer extension studies identified a PruR-dependent promoter responsive to proline in the 5'-flanking region of putA. Thus, the proline utilization system of P. aeruginosa differs from that of P. putida with respect to putA structure, the organization of the putAP genes, and the regulatory mechanism of putA expression.
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PMID:Divergent structure and regulatory mechanism of proline catabolic systems: characterization of the putAP proline catabolic operon of Pseudomonas aeruginosa PAO1 and its regulation by PruR, an AraC/XylS family protein. 1227 Aug 21

NifA, the transcriptional activator of nitrogenase (nif) genes, has up to now been described to be regulated in its activity via the sensor NifL only for members of the gamma-subgroup of the PROTEOBACTERIA: This paper reports a functionally similar NifL-like protein outside this group in Azoarcus sp. strain BH72, a diazotrophic grass endophyte belonging to the beta-subgroup of the PROTEOBACTERIA: Its structural genes for nitrogenase (nifHDK) are regulated in response to combined nitrogen and O(2) and expressed endophytically inside rice roots. In order to characterize nitrogen-regulatory genes, an Azoarcus sp. BH72 genomic library was used to select cosmids that complemented a nifA mutation in Azotobacter vinelandii. Sequence analysis of the 3.4 kb genomic region complementing nifA showed two ORFs with sequence identities of 44% to NifL and 61% to NifA of Azotobacter vinelandii. According to Northern blot and reverse transcriptase PCR analysis, the nifLA transcript was more abundant at low combined nitrogen and O(2) levels, results which were corroborated by GUS (beta-glucuronidase) assays using a transcriptional nifL::gusA fusion. N(2) fixation was abolished in a NifLA(-) and a NifA(-) mutant, wild-type fixation being restored by nifLA in trans. The NifLA(-) mutant also failed to activate nifH::gus expression, indicating that NifA is the obligate transcriptional activator for nifHDK. A nifL mutant was diazotrophic and did not show repression of nifH::gusA by ammonium or O(2), suggesting that NifL of Azoarcus sp. strain BH72 has a similar role in inactivating NifA in response to O(2) and combined nitrogen as NifL in bacteria of the gamma-PROTEOBACTERIA:
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PMID:Identification of a NifL-like protein in a diazotroph of the beta-subgroup of the Proteobacteria, Azoarcus sp. strain BH72. 1236 54

The Azotobacter vinelandii sigma(54)-dependent transcriptional activator protein NifA is regulated by the NifL protein in response to redox, carbon, and nitrogen status. Under conditions inappropriate for nitrogen fixation, NifL inhibits transcription activation by NifA through the formation of the NifL-NifA protein complex. NifL inhibits the ATPase activity of the central AAA+ domain of NifA required to drive open complex formation by sigma(54)-RNA polymerase and may also inhibit the activator-polymerase interaction. To analyze the mechanism of inhibition in greater detail, we isolated NifA mutants which are resistant to the inhibitory action of NifL. Mutations in both the amino-terminal GAF domain and the catalytic AAA+ domain of NifA were isolated. Several mutants blocked inhibition by NifL in response to both nitrogen and redox status, whereas some of the mutant NifA proteins were apparently able to discriminate between the forms of NifL present under different environmental conditions. One mutant protein, NifA-Y254N, was resistant to NifL under conditions of anaerobic nitrogen excess but was relatively sensitive to NifL under aerobic growth conditions. The properties of the purified mutant protein in vitro were consistent with the in vivo phenotype and indicate that NifA-Y254N is not responsive to the nitrogen signal conveyed by the interaction of NifL with A. vinelandii GlnK but is responsive to the oxidized form of NifL when ADP is present. Our observations suggest that different conformers of NifL may be generated in response to discrete signal transduction events and that both the GAF and AAA+ domains of NifA are involved in the response to NifL.
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PMID:Mutant forms of the Azotobacter vinelandii transcriptional activator NifA resistant to inhibition by the NifL regulatory protein. 1244 27

Mimosine is a toxin present in the tree-legume leucaena (Leucaena leucocephala), including its root nodules and the root exudates. The leucaena-nodulating Rhizobium sp. strain TAL1145 degrades mimosine (Mid(+)) and utilizes it as a source of carbon and nitrogen. Twelve TAL1145 mutants defective in mimosine degradation (Mid(-)) were made through Tn3Hogus, TnphoA or kanamycin-resistance-cassette insertions. A 5.0 kb PstI fragment of TAL1145, subcloned from a cosmid clone containing mid genes for mimosine degradation, complemented most of the Mid(-) mutants. Sequencing this fragment and the adjacent 0.9 kb PstI fragment identified five genes, midA, midB, midC, midD and midR, of which the first three genes encode ABC transporter proteins involved in mimosine uptake, while midD encodes an aminotransferase required for degrading mimosine into 3-hydroxy-4-pyridone, and midR is a regulatory gene encoding a LysR-type transcriptional activator. The location of MidA in the periplasm was shown by making two midA : : phoA fusions, which made active alkaline phosphatase in the periplasm. The various mid : : gus and midA : : phoA fusions were inducible by mimosine, and a midD : : gus fusion mutant showed beta-glucuronidase activity in the leucaena nodules, indicating that midD is expressed in the nodules. Similarly, a midA : : phoA fusion expressed alkaline phosphatase activity in the leucaena nodules, indicating that mimosine induces midA transcription in the bacteroids. mid genes are specific for the Mid(+) strains of leucaena Rhizobium and are absent in strains of other Rhizobium, Sinorhizobium and Bradyrhizobium spp.
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PMID:The mid genes of Rhizobium sp strain TAL1145 are required for degradation of mimosine into 3-hydroxy-4-pyridone and are inducible by mimosine. 1262 15

Initiation of meiosis in Saccharomyces cerevisiae is regulated by mating type and nutritional conditions that restrict meiosis to diploid cells grown under starvation conditions. Specifically, meiosis occurs in MATa/MATalpha cells shifted to nitrogen depletion media in the absence of glucose and the presence of a nonfermentable carbon source. These conditions lead to the expression and activation of Ime 1, the master regulator of meiosis. IME1 encodes a transcriptional activator recruited to promoters of early meiosis-specific genes by association with the DNA-binding protein, Ume6. Under vegetative growth conditions these genes are silent due to recruitment of the Sin3/Rpd3 histone deacetylase and Isw2 chromatin remodeling complexes by Ume6. Transcription of these meiotic genes occurs following histone acetylation by Gcn5. Expression of the early genes promote entry into the meiotic cycle, as they include genes required for premeiotic DNA synthesis, synapsis of homologous chromosomes, and meiotic recombination. Two of the early meiosis specific genes, a transcriptional activator, Ndt80, and a CDK2 homologue, Ime2, are required for the transcription of middle meiosis-specific genes that are involved with nuclear division and spore formation. Spore maturation depends on late genes whose expression is indirectly dependent on Ime1, Ime2, and Ndt80. Finally, phosphorylation of Imel by Ime2 leads to its degradation, and consequently to shutting down of the meiotic transcriptional cascade. This review is focusing on the regulation of gene expression governing initiation and progression through meiosis.
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PMID:Transcriptional regulation of meiosis in budding yeast. 1272 50


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