Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.6 (RNA polymerase)
34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Escherichia coli aidB gene is regulated by two different mechanisms, an ada-dependent pathway triggered by methyl damage to DNA and an ada-independent pathway triggered when cells are grown without aeration. In this report we describe our search for mutations affecting the ada-independent aidB induction pathway. The mutant strain identified carries two mutations affecting aidB expression. These mutations are named abrB (aidB regulator) and abrD. The abrB mutation is presently poorly characterized because of instability of the phenotype it imparts. The second mutation, abrD1, reduces the expression of aidB observed when aeration is ceased and oxygen becomes limiting. Genetic and phenotypic analysis of the abrD1 mutation demonstrates that it is an allele of rpoS. Thus, aidB is a member of the family of genes that are transcribed by a sigma S-directed RNA polymerase holoenzyme. Examination of aidB expression in an rpoS insertion mutant strain indicates that both rpoS13::Tn10 and abrD1 mutations reduce aidB expression under oxygen-limiting conditions that prevail in unaerated cultures, reduce aidB induction by acetate at a low pH, but have little or no effect on the ada-dependent alkylation induction of aidB.
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PMID:Induction of the Escherichia coli aidB gene under oxygen-limiting conditions requires a functional rpoS (katF) gene. 800 88

tRNA(2Gln) made in vitro by transcription with T7 RNA polymerase does not contain the pseudouridines at positions 38, 39, and 55, the 4-thiouridine at position 8, or any of the methylated bases found in the tRNA(2Gln) made in vivo. Cocrystals of unmodified tRNA(2Gln) complexed with glutaminyl-tRNA synthetase from Escherichia coli are isomorphous with those of the complex with modified tRNA(2Gln). A difference electron density map between the complexes with modified and unmodified tRNAs calculated at 2.5-A resolution shows no differences in the protein or tRNA structures, except for some very small shifts in atoms contacting the thiol at the 4 position of uridine 8 that are required to accommodate the smaller oxygen in the unmodified tRNA. Perhaps the most functionally significant change in the unmodified tRNA is the absence of the specifically bound water molecules that are observed to cross-link the N5 of the pseudo-uridines to their 5' phosphate. This suggests a possible role for pseudouridinylation in stabilization of the tRNA through water-mediated linking of these modified bases to the backbone, which is consistent with the lower thermal stability of the unmodified tRNA. An identical water-bridging structure is possible at four of the five other psuedo-uridines in known tRNA structures.
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PMID:Crystal structure of unmodified tRNA(Gln) complexed with glutaminyl-tRNA synthetase and ATP suggests a possible role for pseudo-uridines in stabilization of RNA structure. 801 21

FNR is a transcriptional regulator that controls gene expression in response to oxygen limitation in Escherichia coli. The NADH dehydrogenase II gene (ndh) is repressed by FNR under anaerobic conditions. Repression is not simply due to occlusion of the promoter (-35 and -10) region by FNR because adjacent pairs of FNR monomers were found to bind at two sites centred at -50.5 and -94.5 in the ndh promoter region without preventing RNA polymerase binding. However, contact between RNA polymerase and the -132 to -62 region of the non-coding strand of ndh DNA, and RNA polymerase-mediated open complex formation, were prevented by bound FNR. The upstream FNR-binding site (-94.5) was needed for efficient FNR-dependent repression of ndh transcription in vitro, and also for repression of an ndh-lacZ fusion in vivo. Anaerobic ndh repression may thus involve the binding of two pairs of FNR monomers upstream of the -35 region, which prevents essential RNA polymerase-DNA contacts in the upstream region as well as inhibiting RNA polymerase function by direct FNR interaction. Expression of the ndh-lacZ fusion in an fnr deletion strain was enhanced by anaerobic growth in rich medium or minimal medium supplemented with amino acids. Furthermore, two proteins (M(r) 12,000 and 35,000) which interact with and may activate transcription from the ndh promoter under these conditions were detected by gel retardation analysis. These putative amino acid-responsive activators may thus offset FNR-mediated repression and maintain a low level of anaerobic ndh expression for regulating the NAD+/NADH ratio during growth in rich media.
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PMID:Regulation of transcription at the ndh promoter of Escherichia coli by FNR and novel factors. 806 61

This report is concerned with the structural characterization and genetic regulation of new bacterial groES and groEL chaperonin genes, and presents two novelties. The first is the discovery that the nitrogen fixing soybean root nodule bacterium, Bradyrhizobium japonicum, unlike all other prokaryotes investigated so far, possesses a multigene family consisting of five very similar, though not identical, groESL-like genes. The second novelty relates to the finding that these five homologues are expressed to different degrees and, in particular, that one family member (namely groESL3) is induced by a mechanism that does not involve the well-known heat shock response. By contrast, the groESL3 genes are co-regulated together with symbiotic nitrogen fixation genes, in that they are activated by the nitrogen fixation regulatory protein NifA at low oxygen conditions and transcribed from a -24/-12 promoter by the sigma 54 RNA polymerase. Two other members of the groESL gene family are apparently expressed constitutively at different levels, and yet another one is strongly induced by high temperature. As an attractive hypothesis it follows that B. japonicum may modulate its cellular contents of GroES- and GroEL-like chaperonins in response to specific environmental conditions and physiological needs.
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PMID:One member of a gro-ESL-like chaperonin multigene family in Bradyrhizobium japonicum is co-regulated with symbiotic nitrogen fixation genes. 810 85

The prokaryotic enhancer-binding protein NifA stimulates transcription at a distance by binding to sequences upstream of nitrogen fixation (nif) promoters and catalyzing the formation of open promoter complexes by RNA polymerase containing the alternative sigma factor, sigma 54. The activity of NifA in vivo is modulated by the negative regulatory protein NifL in response to environmental oxygen and fixed nitrogen. To date, a detailed biochemical analysis of these proteins from the model diazotroph Klebsiella pneumoniae has been hindered by their insolubility. We have now purified NifA and NifL from Azotobacter vinelandii in their native form. NifA is competent in specific DNA binding, transcriptional activation, and response to negative regulation by NifL in vitro. In contrast to the conserved mechanism of phosphotransfer demonstrated by other two-component regulatory systems, our results support a model in which NifL regulates the activity of NifA via a protein-protein steric block interaction rather than a catalytic modification of NifA.
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PMID:Purification and in vitro activities of the native nitrogen fixation control proteins NifA and NifL. 820 22

Oxygen concentration regulates the expression of nitrogen fixation genes in the symbiotic bacterium Rhizobium meliloti. We demonstrate that two proteins, FixL and FixJ, that belong to the two-component family of regulatory proteins are necessary and sufficient for oxygen-regulated in vitro transcription of the two key regulatory genes, nifA and fixK. We show directly that FixJ is a transcriptional activator, working in conjunction with the RNA polymerase sigma 70 holoenzyme. Addition of FixL122, a soluble form of the sensor FixL protein, to the transcription assay enhanced FixJ transcriptional activity in response to low oxygen concentration. This enhancement of FixJ activity was correlated with FixJ phosphorylation.
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PMID:Oxygen-regulated in vitro transcription of Rhizobium meliloti nifA and fixK genes. 822 29

This paper describes the cytotoxicity of ranunculin (RAN) and its mechanism of action. The IC50 of RAN against the KB and Bel7402 cells in colony test were found to be 0.21 and 0.35 mumol/L respectively. RAN inhibited the incorporation of 3H-labeled precursors into DNA and RNA of L1210 cells. RAN (15 mumol/L) markedly decreased DNA synthesis catalyzed by DNA polymerase I and promoted the generation of superoxide anions in DMSO/KO2 system. In the meantime, SOD and CAT were shown to partly revoke the inhibitory effects of RAN upon the incorporation of 3H-TdR into DNA. No direct reaction between RAN and DNA template was observed and no effect of RAN on DNA TOPO II or RNA polymerase was found. Our results suggest that the cytotoxicity of RAN in vitro may be due to inhibition of DNA polymerase and increase of oxygen free radicals.
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PMID:[The cytotoxicity and action mechanism of ranunculin in vitro]. 823 75

In the free-living diazotroph Klebsiella pneumoniae, the NifA protein is required for transcription of all nif (nitrogen fixation) operons except the regulatory nifLA operon itself. NifA activates transcription of nif operons by the alternative holoenzyme form of RNA polymerase, sigma 54 holoenzyme. In vivo, NifL is known to antagonize the action of NifA in the presence of molecular oxygen or combined nitrogen. We now demonstrate inhibition by NifL in vitro in both a coupled transcription-translation system and a purified transcription system. Crude cell extracts containing NifL inhibit NifA activity in the coupled system, as does NifL that has been solubilized with urea and allowed to refold. Inhibition is specific to NifA in that it does not affect activation by NtrC, a transcriptional activator homologous to NifA, or transcription by sigma 70 holoenzyme. Renatured NifL also inhibits transcriptional activation by a maltose-binding protein fusion to NifA in a purified transcription system, indicating that no protein factor other than NifL is required. Since inhibition in the purified system persists anaerobically, our NifL preparation does not sense molecular oxygen directly.
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PMID:In vitro activity of NifL, a signal transduction protein for biological nitrogen fixation. 824 38

The NIFA protein of Klebsiella pneumoniae is required for transcription of all nif (nitrogen fixation) operons except the regulatory nifLA operon itself. NIFA activates transcription of nif operons by the alternative holoenzyme form of RNA polymerase, sigma 54-holoenzyme, in a nucleoside triphosphate (NTP)-dependent manner. NIFL antagonizes the action of NIFA in the presence of molecular oxygen or combined nitrogen. The NIFA protein of K. pneumoniae is composed of three domains: an N-terminal domain with unclear function, a central catalytic domain, and a C-terminal DNA-binding domain. We report that the isolated central domain of NIFA activates transcription in vitro and that this activation requires NTP with a hydrolyzable beta-gamma bond, as does activation by intact NIFA. Transcriptional activation by the isolated central domain has the heat lability characteristic of intact NIFA and is inhibited by NIFL. The central domain has an NTPase activity that is also heat-labile but is not inhibited by NIFL. Taken together, these results imply that NIFL interferes with contact between NIFA and sigma 54-holoenzyme.
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PMID:The isolated catalytic domain of NIFA, a bacterial enhancer-binding protein, activates transcription in vitro: activation is inhibited by NIFL. 827 50

We have constructed a synthetic photoendonuclease composed of T7 RNA polymerase linked to rose bengal. The promoter-specific polymerase confers site-specific binding, and the photosensitizer rose bengal allows light-induced DNA cleavage. Using a gentle labeling procedure, we find that the polymerase can be labeled with 1-30 rose bengals. Polymerase labeled to about 8 rose bengals per molecule retains the same efficiency and specificity of binding to promoter-containing DNA as unlabeled polymerase. At this level of rose bengal substitution, the synthetic endonuclease, in the presence of visible light, specifically cleaves linear or supercoiled DNA containing a T7 promoter. It induces frank single-strand breaks, rather than labile sites convertible to breaks upon additional treatments. Neither the free rose bengal moiety not bonded to polymerase nor the free (not bound to DNA) rose bengal-substituted polymerase cleaves DNA. Although rose bengal is an efficient generator of singlet oxygen, depletion of oxygen from reaction mixtures increases the cleavage rate. This indicates that singlet oxygen cleavage is not a major mechanism of DNA nicking by the synthetic endonuclease. At higher levels of rose bengal substitution, the labeled polymerase shows decreased binding efficiency and increased nonspecific binding to DNA without a T7 promoter; the specificity of DNA cleavage also decreases. These results indicate that the site specificity of rose bengal photocleavage by the synthetic endonuclease results from specific binding of the polymerase, and thus rose bengal photonicking reflects polymerase binding.
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PMID:Promoter-specific synthetic photoendonuclease: rose bengal-labeled T7 RNA polymerase. 843 39


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