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

Two Bradyrhizobium japonicum nolA mutants were constructed and used to test the functional role of NolA in nodulation. Contrary to the previous hypothesis that NolA acts as a repressor of nod gene transcription, the expression of a nodD1-lacZ or nodY-lacZ fusion in the nolA mutant strains was similar to that found in the wild type. However, NolA does appear to act as a transcriptional regulatory protein since it is required for its own expression, as well as that of nodD2. Expression of NodD2 from a constitutive promoter led to a significant reduction in nodC-lacZ activity. Therefore, the repression of nod gene expression by NolA is likely an indirect effect, perhaps mediated by other genes (e.g., nodD2) that are regulated by NolA. When inoculated onto soybean roots, the nolA mutant strains showed only a slight delay in nodulation as compared to the wild type. However, the mutant strains were grossly defective in nodulation and nitrogen fixation on cowpea plants. Microscopic examination of soybean nodules induced by the nolA mutant strains showed developmental and morphological characteristics similar to nodules formed by the wild type with only a slight delay in bacteroid maturation. In contrast, cowpea nodules induced by the nolA mutant strains contained fewer infected cells and bacteroids were not found in a typical symbiosome structure. These results indicate that NolA is a transcriptional activator required for the expression of genes that play a role not only in the early stages of infection, but also during the later stages of bacteroid development and maintenance.
 ...
PMID:Phenotypic characterization and regulation of the nolA gene of Bradyrhizobium japonicum. 881 78

(1) AUG codons that either permit or prevent 'leaky scanning' of mRNA encoding AREA, the transcriptional activator mediating nitrogen metabolite repression in Aspergillus nidulans, have been identified. The consensus context for a strong initiation codon (i.e. one preventing 'leaky scanning') derived from this work is GXX AUG C/UCX. However, AUG codons which do not conform to this consensus are nevertheless able to initiate translation. (2) Translational reinitiation can occur within areA mRNA, although there is a limitation determined by the distance between the chain termination and reinitiation codons and/or the strength of the reinitiation codon. (3) The minimum size of the region of areA mRNA that is competent for initiation of translation has been determined to be 329 nucleotides (nt), and might be at least 975 nt if a 709 bp deletion does not alter it.
 ...
PMID:Translational initiation competence, 'leaky scanning' and translational reinitiation in areA mRNA of Aspergillus nidulans. 883 Feb 59

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.
 ...
PMID:Symbiotic nitrogen fixation does not require adenylylation of glutamine synthetase I in Rhizobium meliloti. 893 24

The nifLA operon of Klebsiella pneumoniae codes for the two antagonistic regulatory proteins which control expression of all other nitrogen fixation genes. NifA is a transcriptional activator, and NifL inhibits NifA. The importance of a correct NifL-NifA stoichiometry for efficient regulation of nitrogen fixation genes has been investigated by constructing a strain with an altered nifL-nifA gene dosage ratio, resulting from the integration of an extra copy of nifA. Results showed that a balanced synthesis of both gene products is essential for correct regulation. Effects of mutations provoking translation termination of nifL upstream or downstream of its natural stop codon, combined with overproduction of both proteins when the genes are transcribed and translated from signals of the phi10 gene of the phage T7, showed that, in addition to the previously reported transcriptional polarity, there is translational coupling between nifL and nifA. In spite of the apparently efficient ribosome binding site of nifA, its rate of independent translation is very low. This is due to a secondary structure masking the Shine-Dalgarno sequence of nifA, which could be melted by ribosomes translating nifL. Mutational analysis confirmed the functional significance of the secondary structure in preventing independent translation of nifA. Translational coupling between the two cistrons is proposed as an efficient mechanism to prevent production of an excess of NifA, which would affect the normal regulation of nitrogen fixation genes.
 ...
PMID:Mechanism of coordinated synthesis of the antagonistic regulatory proteins NifL and NifA of Klebsiella pneumoniae. 895 2

In Salmonella typhimurium, transcription of the glnA gene (encoding glutamine synthetase) is under the control of the nitrogen-regulatory (ntr) system comprising the alternate sigma factor sigma54 (NtrA) and the two-component sensor-transcriptional activator pair NtrB and NtrC. The glnA, ntrB, and ntrC genes form an operon. We measured the virulence of S. typhimurium strains with nitrogen-regulatory mutations after intraperitoneal (i.p.) or oral inoculations of BALB/c mice. Strains with single mutations in glnA, ntrA, ntrB, or ntrC had i.p. 50% lethal doses (LD50s) of <10 bacteria, similar to the wild-type strain. However, a strain with a delta(glnA-ntrC) operon deletion had an i.p. LD50 of >10(5) bacteria, as did delta glnA ntrA and delta glnA ntrC strains, suggesting that glnA strains require an ntr-transcribed gene for full virulence. High-level transcription of the glutamine transport operon (glnHPQ) is dependent upon both ntrA and ntrC, as determined by glnHp-lacZ fusion measurements. Moreover, delta glnA glnH and delta glnA glnQ strains are attenuated, similar to delta glnA ntrA and delta glnA ntrC strains. These results reveal that access of S. typhimurium to host glutamine depends on the ntr system, which apparently is required for the transcription of the glutamine transport genes. The delta(glnA-ntrC) strain exhibited a reduced ability to survive within the macrophage cell line J774, identifying a potential host environment with low levels of glutamine. Finally, the delta(glnA-ntrC) strain, when inoculated at doses as low as 10 organisms, provided mice with protective immunity against challenge by the wild-type strain, demonstrating its potential use as a live vaccine.
 ...
PMID:Simultaneous prevention of glutamine synthesis and high-affinity transport attenuates Salmonella typhimurium virulence. 900 17

Nitrite reductase catalyzes the reduction of nitrite to nitric oxide, the first step in denitrification to produce a gaseous product. We have cloned the gene nirK, which encodes the copper-type nitrite reductase from a denitrifying variant of Rhodobacter sphaeroides, strain 2.4.3. The deduced open reading frame has significant identity with other copper-type nitrite reductases. Analysis of the promoter region shows that transcription initiates 31 bases upstream of the translation start codon. The transcription initiation site is 43.5 bases downstream of a putative binding site for a transcriptional activator. Maximal expression of a nirK-lacZ construct in 2.4.3 requires both a low level of oxygen and the presence of a nitrogen oxide. nirK-lacZ expression was severely impaired in a nitrite reductase-deficient strain of 2.4.3. This suggests that nirK expression is dependent on nitrite reduction. The inability of microaerobically grown nitrite reductase-deficient cells to induce nirK-lacZ expression above basal levels in medium unamended with nitrate demonstrates that changes in oxygen concentrations are not sufficient to modulate nirK expression.
 ...
PMID:Characterization and regulation of the gene encoding nitrite reductase in Rhodobacter sphaeroides 2.4.3. 902 88

Rhizobium leguminosarum bv. viciae expresses an uptake hydrogenase in symbiosis with peas (Pisum sativum) but, unlike all other characterized hydrogen-oxidizing bacteria, cannot express it in free-living conditions. The hydrogenase-specific transcriptional activator gene hoxA described in other species was shown to have been inactivated in R. leguminosarum by accumulation of frameshift and deletion mutations. Symbiotic transcription of hydrogenase structural genes hupSL originates from a -24/-12 type promoter (hupSp). A regulatory region located in the -173 to -88 region was essential for promoter activity in R. leguminosarum. Activation of hupSp was observed in Klebsiella pneumoniae and Escherichia coli cells expressing the K. pneumoniae nitrogen fixation regulator NifA, and in E. coli cells expressing R. meliloti NifA. This activation required direct interaction of NifA with the essential -173 to -88 regulatory region. However, no sequences resembling known NifA-binding sites were found in or around this region. NifA-dependent activation was also observed in R. etli bean bacteroids. NifA-dependent hupSp activity in heterologous hosts was also absolutely dependent on the RpoN sigma-factor and on integration host factor. Proteins immunologically related to integration host factor were identified in R. leguminosarum. The data suggest that hupSp is structurally and functionally similar to nitrogen fixation promoters. The requirement to coordinate nitrogenase-dependent H2 production and H2 oxidation in nodules might be the reason for the loss of HoxA in R. leguminosarum and the concomitant NifA control of hup gene expression. This evolutionary acquired control would ensure regulated synthesis of uptake hydrogenase in the most common H2-rich environment for rhizobia, the legume nodule.
 ...
PMID:Hydrogenase genes from Rhizobium leguminosarum bv. viciae are controlled by the nitrogen fixation regulatory protein nifA. 917 61

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.
 ...
PMID:Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K. 920 62

The maize (Zea mays L.) b-ZIP transcriptional activator Opaque-2(O2) regulates the synthesis of major endosperm proteins. In the o2 homozygote, 22 kDa zein prolamins and the b-32 ribosome-inactivating protein are greatly reduced in level. An in vitro endosperm culture system has been studied in which o2 endosperm synthesizes 22 kDa zein and b-32 in response to nitrogen supplements. An increase in 22 kDa zein mRNA concentration is also seen, implying an effect at the level of transcription or differential RNA turnover. The nitrogen-dependent induction of 22 kDa zein synthesis in cultured o2 endosperm was further investigated by analysing transient expression of reporter constructs. The highest response to nitrogen was exhibited by the intact 22 kDa zein promoter. Removal of individual O2 binding sites either reduced or increased overall promoter activity, but always decreased the nitrogen-dependent stimulation of activity. This effect was observed equally in wild-type and o2 mutant endosperm. It is concluded that a factor other then O2 is responsible for activating the 22 kDa zein promoter under high-nitrogen culture conditions. Despite its occurrence in the absence of O2 protein, the nitrogen response is mediated through binding at O2 binding sites. An induction of 22 kDa zein and b-32 synthesis in cultured o2 endosperm could also be achieved on nitrogen-free media by the addition of abscisic acid or methyl jasmonate.
 ...
PMID:Nitrogen and hormonal responsiveness of the 22 kDa alpha-zein and b-32 genes in maize endosperm is displayed in the absence of the transcriptional regulator Opaque-2. 930 Oct 81

An early process in the pathogenesis of enteric bacteria is colonization of the intestinal epithelium leading to local multiplication, pathophysiological interactions with the host and further spreading. Attachment is typically mediated by bacterial fimbriae, which are selectively expressed during growth in the intestine. Here we report an analysis of the regulation of 987P fimbrial expression of enterotoxigenic Escherichia coli (ETEC). Expression of both fasH, the transcriptional activator of the 987P fimbrial genes, and fasA, the major fimbrial subunit, is regulated in response to a variety of environmental stimuli. We have found that expression of fasH is regulated in response to the carbon status of the growth medium by the cAMP-CRP complex. Moreover, fasH is regulated in response to both the nitrogen status of the growth medium and the external pH. Expression of fasA is activated by FasH, and is also selectively regulated in response to growth temperature by HNS. Regulation of fimbrial expression by carbon and/or nitrogen gradients is proposed to provide a mechanism that allows preferential colonization of different segments of the intestine by various enteropathogens, such as ETEC, enteropathogenic E. coli and Vibrio cholerae.
 ...
PMID:Differential regulation of fasA and fasH expression of Escherichia coli 987P fimbriae by environmental cues. 937 7


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>