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 plastid DNA of Neospora caninum encodes a homologue of the rpoB gene, which is believed to encode a subunit of a bacterial or chloroplast-like RNA polymerase. The predicted protein product of the N. caninum rpoB gene has three in-frame UGA codons which appear to encode tryptophan residues rather than act as stop codons. Based on the nucleotide sequence of a portion of the ssrRNA gene of the N. caninum plastid, a model for suppression of UGA termination in this plastid is presented.
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PMID:Sequence evidence for an altered genetic code in the Neospora caninum plastid. 1060 42

UV resistance of bacterial endospores derives from a unique DNA photochemistry in which the major UV photoproduct is the thymine dimer 5-thyminyl-5,6-dihydrothymine (spore photoproduct [SP]) instead of cyclobutane pyrimidine dimers. Repair of SP during spore germination is due in large part to the activity of the enzyme SP lyase encoded by splB, the second cistron of the splAB operon. Expression of the splAB operon in Bacillus subtilis is transcriptionally activated by the Esigma(G) form of RNA polymerase during morphological stage III in the developing forespore compartment, and SP lyase is packaged into the dormant spore. In addition to temporal and compartmental control of splAB expression, a second regulatory circuit which modulates the level of expression of splB-lacZ fusions without altering their developmental timing or compartmentalization is reported here. This second regulatory circuit involves the negative action of the splA gene product, a 79-amino-acid protein with approximately 50% similarity and 17% identity to TRAP, the tryptophan RNA-binding attenuation protein from B. subtilis and Bacillus pumilus.
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PMID:The TRAP-like SplA protein is a trans-acting negative regulator of spore photoproduct lyase synthesis during Bacillus subtilis sporulation. 1062 12

The amino-terminal arginine-rich motif of the phage HK022 Nun protein binds phage lambda nascent mRNA transcripts while the carboxy-terminal domain binds RNA polymerase and arrests transcription. The role of specific residues in the carboxy-terminal domain in transcription termination were investigated by mutagenesis, in vitro and in vivo functional assays, and NMR spectroscopy. Coordination of zinc to three histidine residues in the carboxy-terminus inhibited RNA binding by the amino-terminal domain; however, only two of these histidines were required for transcription arrest. These results suggest that additional zinc-coordinating residues are supplied by RNA polymerase in the context of the Nun-RNA polymerase complex. Substitution of the penultimate carboxy-terminal tryptophan residue with alanine or leucine blocks transcription arrest, whereas a tyrosine substitution is innocuous. Wild-type Nun fails to arrest transcription on single-stranded templates. These results suggest that Nun inhibition of transcription elongation is due in part to interactions between the carboxy-terminal tryptophan of Nun and double-stranded DNA, possibly by intercalation. A model for the termination activity of Nun is developed on the basis of these data.
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PMID:The carboxyl terminus of phage HK022 Nun includes a novel zinc-binding motif and a tryptophan required for transcription termination. 1073 32

The association of monomeric TATA binding protein with promoter DNA is an essential first step in many current models of eukaryotic transcription initiation. This step is followed by others in which additional transcription factors, and finally RNA polymerase, assemble at the promoter. Here we characterize the quaternary interactions of the Saccharomyces cerevisiae TATA-binding protein (yTBP), in the absence of other proteins or DNA. The data reveal a robust pattern in which yTBP monomers equilibrate with tetramers and octamers over a broad span of temperatures (4 degrees C </= T </= 37 degrees C) and salt concentrations (60 mM </= [KCl] </= 1 M), that includes the physiological range. Association is highly cooperative, with octamer formation favored by approximately 9 kcal/mol over tetramer formation. Changes in association constant with [KCl] are consistent with an assembly-linked release of ions at low salt and an assembly-linked uptake of ions at high salt, for both monomer right arrow over left arrow tetramer and tetramer right arrow over left arrow octamer reaction steps. Fluorescence emission spectra and steady-state anisotropies reveal that the amino-terminal domain changes conformation and dynamics at both association steps and that the polarity of the environment near tryptophan 26 is sensitive to changes in [KCl] in the monomeric and tetrameric states but not the octameric state. These results are consistent with a [salt]-dependent change in the assembly mechanism near 300 mM KCl and suggest that the amino-terminal domain may modulate the self-association of the full-length protein. TBP self-association may regulate many of its cellular functions, including transit of the nuclear membrane and participation in transcription initiation.
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PMID:Participation of the amino-terminal domain in the self-association of the full-length yeast TATA binding protein. 1076 45

Bacillus subtilis DB1005 is a temperature-sensitive (Ts) sigA mutant containing double-amino-acid substitutions (I198A and I202A) on the hydrophobic face of the promoter -10 binding helix of sigma(A) factor. We have analyzed the structural and functional properties of this mutant sigma(A) factor both in vivo and in vitro. Our data revealed that the Ts sigma(A) factor possessed predominantly a multimeric structure which was prone to aggregation at restrictive temperature. The extensive aggregation of the Ts sigma(A) resulted in a very low core-binding activity of the Ts sigma(A) factor and a markedly reduced sigma(A)-RNA polymerase activity in B. subtilis DB1005, suggesting that extensive aggregation of the Ts sigma(A) is the main trigger for the temperature sensitivity of B. subtilis DB1005. Partial proteolysis, tryptophan fluorescence and 1-anilinonaphthalene-8-sulfonate-binding analyses revealed that the hydrophobic face of the promoter -10 binding helix and also the hydrophobic core region of the Ts sigma(A) factor were readily exposed on the protein surface. This hydrophobic exposure provides an important cue for mutual interaction between molecules of the Ts sigma(A) and allows the formation of multimeric Ts sigma(A). Our results also indicate that Ile-198 and Ile-202 on the hydrophobic face of the promoter -10 binding helix are essential to ensure the correct folding and stabilization of the functional structure of sigma(A) factor.
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PMID:Structural and functional properties of a Bacillus subtilis temperature-sensitive sigma(A) factor. 1089 85

The equilibrium binding and kinetics of assembly of the DNA-dependent RNA polymerase (RNAP) sigma(N)-holoenzyme has been investigated using biosynthetically labelled 7-azatryptophyl- (7AW)sigma(N). The spectroscopic properties of such 7AW proteins allows their absorbance and fluorescence to be monitored selectively, even in the presence of high concentrations of other tryptophan-containing proteins. The 7AWsigma(N) retained its biological activity in stimulating transcription from sigma(N)-specific promoters, and in in vitro gel electrophoresis assays of binding to core RNAP from Escherichia coli. Furthermore, five Trp-->Ala single mutants of sigma(N) were shown to support growth under conditions of nitrogen limitation, and showed comparable efficiency in activating the sigma(N)-dependent nifH promoter in vivo, indicating that none of the tryptophan residues were essential for activity. The equilibrium binding of 7AWsigma(N) to core RNAP was examined by analytical ultracentrifugation. In sedimentation equilibrium experiments, absorbance data at 315 nm (which reports selectively on the distribution of free and bound 7AWsigma(N)) established that a 1:1 complex was formed, with a dissociation constant lower than 2 microM. The kinetics of the interaction between 7AWsigma(N) and core RNAP was investigated using stopped-flow spectrofluorimetry. A biphasic decrease in fluorescence intensity was observed when samples were excited at 280 nm, whereas only the slower of the two phases was observed at 315 nm. The kinetic data were analysed in terms of a mechanism in which a fast bimolecular association of sigma(N) with core RNAP is followed by a relatively slow isomerization step. The consequences of these findings on the competition between sigma(N) and the major sigma factor, sigma(70), in Escherichia coli are discussed.
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PMID:Interaction of sigma factor sigmaN with Escherichia coli RNA polymerase core enzyme. 1108 49

The cap-dependent endonuclease of the influenza viral RNA polymerase, which produces the capped RNA primers that initiate viral mRNA synthesis, is comprised of two active sites, one for cap binding and one for endonuclease cleavage. We identify the amino acid sequences that constitute these two active sites and demonstrate that they are located on different polymerase subunits. Binding of the 5' terminal sequence of virion RNA (vRNA) to the polymerase activates a tryptophan-rich, cap-binding sequence on the PB2 subunit. At least one of the tryptophans functions in cap binding, indicating that this active site is probably similar to that of other known cap-binding proteins. Endonuclease cleavage, which is activated by the subsequent binding of the 3' terminal sequence of vRNA, resides in a PB1 sequence that contains three essential acidic amino acids, similar to the active sites of other enzymes that cut polynucleotides to produce 3'-OH ends. These results, coupled with those of our previous study, provide a molecular map of the five known essential active sites of the influenza viral polymerase.
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PMID:The active sites of the influenza cap-dependent endonuclease are on different polymerase subunits. 1129 40

RNA helicase A (RHA) is a member of an ATPase/DNA and RNA helicase family and is a homologue of Drosophila maleless protein (MLE), which regulates X-linked gene expression. RHA is also a component of holo-RNA polymerase II (Pol II) complexes and recruits Pol II to the CREB binding protein (CBP). The ATPase and/or helicase activity of RHA is required for CREB-dependent transcription. To further understand the role of RHA on gene expression, we have identified a 50-amino-acid transactivation domain that interacts with Pol II and termed it the minimal transactivation domain (MTAD). The protein sequence of this region contains six hydrophobic residues and is unique to RHA homologues and well conserved. A mutant with this region deleted from full-length RHA decreased transcriptional activity in CREB-dependent transcription. In addition, mutational analyses revealed that several tryptophan residues in MTAD are important for the interaction with Pol II and transactivation. These mutants had ATP binding and ATPase activities comparable to those of wild-type RHA. A mutant lacking ATP binding activity was still able to interact with Pol II. In CREB-dependent transcription, the transcriptional activity of each of these mutants was less than that of wild-type RHA. The activity of the double mutant lacking both functions was significantly lower than that of each mutant alone, and the double mutant had a dominant negative effect. These results suggest that RHA could independently regulate CREB-dependent transcription either through recruitment of Pol II or by ATP-dependent mechanisms.
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PMID:Dual roles of RNA helicase A in CREB-dependent transcription. 1141 26

Expression of the tryptophanase (tna) operon in Escherichia coli is regulated by catabolite repression and tryptophan-induced transcription antitermination. The key feature of this antitermination mechanism has been shown to be the retention of uncleaved TnaC-peptidyl-tRNA in the translating ribosome. This ribosome remains stalled at the tna stop codon and blocks the access of Rho factor to the tna transcript, thereby preventing transcription termination. In normal S-30 preparations, synthesis of a TnaC peptide containing arginine instead of tryptophan at position 12 (Arg(12)-TnaC) was shown to be insensitive to added tryptophan, i.e. Arg(12)-TnaC-peptidyl-tRNA was cleaved, and there was normal Rho-dependent transcription termination. When the S-30 extract used was depleted of release factor 2, Arg(12)-TnaC-tRNA(Pro) was accumulated in the absence or presence of added tryptophan. Under these conditions the accumulation of Arg(12)-TnaC-tRNA(Pro) prevented Rho-dependent transcription termination, mimicking normal induction. Using a minimal in vitro transcription system consisting of a tna template, RNA polymerase, and Rho, it was shown that RNA sequences immediately adjacent to the tnaC stop codon, the presumed boxA and rut sites, contributed most significantly to Rho-dependent termination. The tna boxA-like sequence appeared to serve as a segment of the Rho "entry" site, despite its likeness to the boxA element.
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PMID:Analysis of tryptophanase operon expression in vitro: accumulation of TnaC-peptidyl-tRNA in a release factor 2-depleted S-30 extract prevents Rho factor action, simulating induction. 1188 Mar 83

The crystal structure of Thermus aquaticus RNA polymerase holoenzyme (alpha2betabeta'omegasigmaA) complexed with a fork-junction promoter DNA fragment has been determined by fitting high-resolution x-ray structures of individual components into a 6.5-angstrom resolution map. The DNA lies across one face of the holoenzyme, completely outside the RNA polymerase active site channel. All sequence-specific contacts with core promoter elements are mediated by the sigma subunit. A universally conserved tryptophan is ideally positioned to stack on the exposed face of the base pair at the upstream edge of the transcription bubble. Universally conserved basic residues of the sigma subunit provide critical contacts with the DNA phosphate backbone and play a role in directing the melted DNA template strand into the RNA polymerase active site. The structure explains how holoenzyme recognizes promoters containing variably spaced -10 and -35 elements and provides the basis for models of the closed and open promoter complexes.
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PMID:Structural basis of transcription initiation: an RNA polymerase holoenzyme-DNA complex. 1201 7


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