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)

We have developed a system for analysis of discrete steps in vaccinia virus early mRNA synthesis during a single round of transcription in vitro. A synthetic early promoter is used to direct transcription by vaccinia RNA polymerase of a G-less cassette in linear duplex DNA. Omission of GTP from transcription reactions leads to the formation of ternary elongation complexes paused stably at the end of the G-less cassette. These complexes can be induced to elongate by provision of GTP. While initiation of transcription is sensitive to low concentrations of salt and Sarkosyl, elongation is relatively resistant to these agents. Termination can be studied in a single synthetic cycle by forming transcription complexes paused just proximal to the termination signal TTTTTNT that can subsequently elongate and terminate. By selectively incorporating the termination-inhibiting analog BrUMP into proximal and distal portions of the nascent transcript, we localize the termination signal within or near the sequence UUUUUNU in the nascent RNA. We show that access of the vaccinia termination factor (VTF/capping enzyme) to the transcriptional apparatus can occur subsequent to initiation and synthesis of a 390-nucleotide nascent RNA. Termination is more sensitive to inhibition by salt and Sarkosyl than in elongation. This sensitivity is not reversed by preincubation of VTF with the transcription complex. Finally, we confirm the identity of VTF and vaccinia mRNA capping enzyme by demonstration of VTF activity associated with capping enzyme expressed in Escherichia coli.
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PMID:Discrete functional stages of vaccinia virus early transcription during a single round of RNA synthesis in vitro. 171 78

Termination of transcription in vitro by purified vaccinia virus RNA polymerase occurs downstream of a cis-acting signal UUUUUNU in the nascent RNA strand and requires a trans-acting termination factor, VTF, that is associated with the viral mRNA capping enzyme. Factor-dependent termination can be inhibited specifically by incorporation of BrUMP (from BrUTP) into nascent RNA in place of UMP. The relevance of VTF action to early vaccinia mRNA biogenesis was demonstrated in the present study of the effects of BrUTP on mRNA synthesis and release by permeabilized vaccinia virions. BrUMP incorporation inhibited the release of newly made transcripts from the virus particle, resulting in the accumulation of transcripts within virus cores. This effect was observed also with IUMP, but not with BrCMP or IMP incorporation. Transcripts synthesized in the presence of BrUTP were heterogeneous in size and severalfold larger than transcripts made in the presence of UTP. The progressive increase in the size of the core-associated, BrUMP-containing transcripts indicated that they were still engaged by elongating RNA polymerase. These results are consistent with a predominant pathway of mRNA 3'-end formation by virions that involves VTF-dependent transcription termination. These data do not support an alternative model of 3'-end formation by endonucleolytic cleavage of larger RNA precursors.
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PMID:Bromouridine triphosphate inhibits transcription termination and mRNA release by vaccinia virions. 259 81

Reovirus mRNAs synthesized by the virion-associated RNA polymerase contain a 5'-terminal cap that is added to nascent transcripts by polypeptide lambda 2, a structural component of virions encoded by double-stranded RNA genome segment L2. The complete, 3916-nucleotide sequence of a full-length reovirus type 3 L2 DNA clone was determined by the dideoxy chain terminator method. The sequence has a single long open reading frame extending from the second A-T-G at nucleotide 14 to a termination codon at position 3881. On this basis, the 1289-amino acid sequence of polypeptide lambda 2, the reovirus mRNA guanylyltransferase, was deduced and compared to other GTP-binding proteins. Two different, lysine-containing lambda 2 peptide sequences closely resemble predicted amino acid stretches in vaccinia virus guanylyltransferase and potentially form part of active sites in the viral mRNA capping enzymes.
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PMID:Complete nucleotide sequence of reovirus L2 gene and deduced amino acid sequence of viral mRNA guanylyltransferase. 282 87

Transcription termination in vitro by vaccinia RNA polymerase is dependent on a trans-acting factor, VTF, that is associated with, if not identical to, the vaccinia mRNA capping enzyme. VTF-induced termination occurs approximately 50 nucleotides downstream of a signal sequence TTTTTNT in the non-transcribed templated strand; thus the cognate sequence UUUUUNU is expressed in the nascent RNA. To address the role of the nascent RNA in chain termination, the effects of nucleotide base analog substitutions were studied. Incorporation of bromo- (Br) UMP or iodo- (I) UMP into RNA abrogated factor-dependent termination without preventing the synthesis of read-through transcripts. Substitution of either ITP or 7'-methylguanosine for GTP did not inhibit factor-dependent termination, nor did the substitution of BrCTP or ICTP for CTP. The early transcripts synthesized in vitro were sensitive to RNase T2 but resistant to RNase H, indicating an absence of extensive hybridization of RNA product to the DNA template. Substitution of BrUTP for UTP did not alter the nuclease sensitivity of the transcripts, suggesting that increased stability of RNA:DNA hybrid structures did not account for the analog effects. These results are consistent with a model in which recognition of the primary sequence UUUUUNU in nascent RNA by the polymerase and/or VTF is required for transcription termination.
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PMID:Factor-dependent transcription termination by vaccinia virus RNA polymerase. Evidence that the cis-acting termination signal is in nascent RNA. 283 68

A high-molecular-weight protein complex that is capable of accurate transcription initiation and termination of vaccinia virus early genes without additional factors was demonstrated. The complex was solubilized by disruption of purified virions, freed of DNA by passage through a DEAE-cellulose column, and isolated by glycerol gradient sedimentation. All detectable RNA polymerase activity was associated with the transcription complex, whereas the majority of enzymes released from virus cores including mRNA (nucleoside-2'-O)methyltransferase, poly(A) polymerase, topoisomerase, nucleoside triphosphate phosphohydrolase II, protein kinase, and single-strand DNase sedimented more slowly. Activities corresponding to two enzymes, mRNA guanylyltransferase (capping enzyme) and nucleoside triphosphate phosphohydrolase I (DNA-dependent ATPase), partially sedimented with the complex. Silver-stained polyacrylamide gels, immunoblots, and autoradiographs confirmed the presence of subunits of vaccinia virus RNA polymerase, mRNA guanylyltransferase, and nucleoside triphosphate phosphohydrolase I, as well as additional unidentified polypeptides, in fractions with transcriptase activity. A possible role for the DNA-dependent ATPase was suggested by studies with ATP analogs with gamma-S or nonhydrolyzable beta-gamma-phosphodiester bonds. These analogs were used by vaccinia virus RNA polymerase to nonspecifically transcribe single-stranded DNA templates but did not support accurate transcription of early genes by the complex. Transcription also was sensitive to high concentrations of novobiocin; however, this effect could be attributed to inhibition of RNA polymerase or ATPase activities rather than topoisomerase.
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PMID:Sedimentation of an RNA polymerase complex from vaccinia virus that specifically initiates and terminates transcription. 303 83

A DNA-dependent RNA polymerase that transcribes vaccinia virus early genes was partially purified from virus cores by deoxycholate extraction and DEAE-cellulose column chromatography. Accurately initiated and terminated RNAs were synthesized by this enzyme in the presence of a linear duplex DNA template. Glycerol gradient sedimentation resolved the in vitro transcription system into two components: fraction I, a rapidly sedimenting RNA polymerase that initiated transcription at an early promoter but transcribed beyond the in vivo 3' terminus to yield a run-off transcript, and fraction II, a more slowly sedimenting fraction, itself devoid of RNA polymerase, that restored efficient termination when added back to fraction I. The termination factor was heat-labile, resistant to N-ethylmaleimide, and did not exhibit endonucleolytic activity on run-off transcripts. Factor-dependent termination required specific sequence information upstream of the site of termination. The vaccinia termination factor was purified extensively by column chromatography on DEAE-cellulose, heparin-agarose, phosphocellulose, and DNA-agarose, and by velocity sedimentation in a glycerol gradient. At each step, termination factor copurified with the vaccinia mRNA capping enzyme. The preparation was well over 90% pure with respect to the latter enzyme, suggesting that termination activity was tightly associated with, if not intrinsic to, the capping enzyme. Nonetheless, formation of the 5'-cap structure did not appear to be a prerequisite for termination.
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PMID:Purification and characterization of a transcription termination factor from vaccinia virions. 362 64

From submerged cultures of Lachnella villosa, Lachnella sp. 541, and Peniophora laeta we isolated marasmic acid (1), a metabolite first described from surface cultures of Marasmius conigenus. The sesquiterpenoid exhibits potent antimicrobial and cytotoxic properties. In cells of the ascitic form of Ehrlich carcinoma RNA and DNA syntheses are preferentially inhibited. Marasmic acid inhibits RNA synthesis in isolated nuclei, but does not interfere with the transport of nucleoside precursors into the cells. RNA polymerase II and capping enzyme (mRNA guanylyltransferase), two enzymes of nucleic acid metabolism, are markedly affected after preincubation with marasmic acid. We assume that marasmic acid acts on nucleic acid syntheses by direct inhibition of some of the enzymes involved. This mode of action would also explain its mutagenic properties. The preparation and testing of two derivatives, 2 and 3, revealed that the alpha,beta-unsaturated aldehyde is essential for the antimicrobial and cytotoxic activity of marasmic acid.
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PMID:Antibiotics from basidiomycetes. XVII. The effect of marasmic acid on nucleic acid metabolism. 630 12

mRNA guanylyltransferase has been extensively purified from calf thymus. A GTP-binding assay was used based on the observations by Shuman and Hurwitz (1981) and Venkatesan and Moss (1982) that vaccinia virus and HeLa cell mRNA guanylyltransferases bind the GMP moiety from GTP in the absence of an acceptor RNA. The mol. wt. of the purified enzyme from calf thymus, estimated by polyacrylamide gel electrophoresis in the presence of SDS, is 65 000. The major protein in the purified enzyme fraction comigrates with the peptide labelled with GMP. Based on scans of silver-stained polyacrylamide gels, mRNA guanylyltransferase constitutes greater than 50% of the protein in these fractions. The enzyme catalyzed the guanylylation at the 5' end of poly(A) with a mixture of diphosphate and triphosphate ends. No evidence was obtained for a direct interaction between mRNA guanylyltransferase and RNA polymerase B (II).
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PMID:Purification of mRNA guanylyltransferase from calf thymus. 632 86

Transcription termination by vaccinia virus RNA polymerase during synthesis of early mRNAs requires a virus-encoded termination factor (VTF). VTF is but one of many activities associated with the vaccinia virus mRNA capping enzyme, a heterodimer of 95- and 33-kDa subunits encoded by the D1 and D12 genes, respectively. Although the three catalytic domains involved in cap formation have been assigned to individual subunits or portions thereof, the structural requirements for VTF activity are unknown. We now report that both full-length subunits are required for transcription termination. The 844-amino acid D1 subunit by itself, which is fully active in triphosphatase and guanylyltransferase functions, has no demonstrable VTF activity in vitro. Neither does the D12 subunit by itself. The heterodimeric methyltransferase domain of D1 (residues 498 to 844) and D12 subunits also has no VTF activity. VTF is not affected by a K-to-M mutation of the guanylyltransferase active site at position 260 (K260M) that abolishes enzyme-GMP complex formation or by a H682A/Y683A double mutation of the D1 subunit, which abrogates methyltransferase activity. Thus, the structural requirements for termination are distinct from those for nucleotidyl transfer and methyl transfer.
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PMID:The D1 and D12 subunits are both essential for the transcription termination factor activity of vaccinia virus capping enzyme. 774 34

An established cell line, clone 64, in which the expression of the RNA polymerase PB1 and PA subunit genes and the nucleoprotein (NP) gene but not the PB2 subunit gene of influenza virus can be induced by the addition of dexamethasone, was used to analyze the replication and transcription machineries of the influenza virus. Both NS-CATc and NS-CATv, the chimeric nonstructural protein chloramphenicol acetyltransferase (NS-CAT) RNAs in the sense and antisense orientations positioned between the 5'- and 3'-terminal sequences of influenza virus RNA segment 8 (the NS gene), respectively, can be transcribed into the corresponding complementary-strand RNA in clone 64 cells only when treated with dexamethasone. Although sense-strand poly(A)+ CAT RNA was detected in the dexamethasone-treated clone 64 cells transfected with NS-CATv RNA, CAT activity was not detected in these cells and the isolated poly(A)+ CAT RNA was inert in an in vitro translation system. However, when the poly(A)+ CAT RNA was capped by using a purified yeast mRNA capping enzyme (mRNA guanylyltransferase), the capped poly(A)+ CAT RNA became translatable in the in vitro translation system. These results indicated that PB1, PA, and NP can support the replication of the influenza virus genome as well as the transcription to yield uncapped poly(A)+ RNA and that PB2 is specifically required for the synthesis of capped RNA.
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PMID:The RNA polymerase PB2 subunit is not required for replication of the influenza virus genome but is involved in capped mRNA synthesis. 781 36


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