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)

RNA synthesis carried out in vitro by Escherichia coli RNA polymerase was inhibited irreversibly by captan when T7 DNA was used as template. An earlier report and this one show that captan blocks the DNA binding site on the enzyme. Herein, it is also revealed that captan acts at the nucleoside triphosphate (NTP) binding site, and kinetic relationships of the action of captan at the two sites are detailed. The inhibition by captan via the DNA binding site of the enzyme was confirmed by kinetic studies and it was further shown that [14C]captan bound to the beta' subunit of RNA polymerase. This subunit contains the DNA binding site. Competitive-like inhibition by captan versus UTP led to the conclusion that captan also blocked the NTP binding site. In support of this conclusion, [14C]captan was observed to bind to the beta subunit which contains the NTP binding site. Whereas, preincubation of RNA polymerase with both DNA and NTPs prevented captan inhibition, preincubation with either DNA or NTPs alone was insufficient to protect the enzyme from the action of captan. Furthermore, the interaction of [14C]captan with the beta and beta' subunits was not prevented by a similar preincubation. Captan also bound, to a lesser extent, to the alpha and sigma subunits. Therefore, captan binding appears to involve interaction with RNA polymerase at sites in addition to those for DNA and NTP; however, this action does not inhibit the polymerase activity.
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PMID:Inhibition of RNA polymerase by captan at both DNA and substrate binding sites. 128 5

Captan (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) was examined for its effects on bovine liver nuclear RNA synthesis. Transcription was measured by [3H] UTP incorporation into either acid insoluble product or isolated RNA. Captan (1 mM) was found to inhibit RNA synthesis 50% in intact nuclei and 70% in a hypotonic lysate of nuclei. Individual RNA polymerase activities were distinguished in both intact nuclei and hypotonic lysate by alpha-amanitin sensitivity. Captan inhibited RNA polymerase I and II activities to an equal extent in both intact and lysate systems. The sulfhydryl compound dithiothreitol (DTT) protected the RNA polymerase activities from inhibition by captan. Initiation of transcription in intact nuclei was measured by [gamma-32P] ATP incorporation into purified RNA and was found to be inhibited 75% by 1 mM captan. This report describes the inhibition of nuclear RNA polymerase activities by captan and suggests a possible mechanism for its toxic effect on eukaryotic polymerases.
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PMID:Initiation of transcription in nuclei is inhibited by captan. 241 83

Captan (N-trichloromethylthiocyclohex-4-ene-1,2-dicarboximide) was shown to inhibit RNA synthesis in vitro catalysed by Escherichia coli RNA polymerase. Incorporation of [gamma-32P]ATP and [gamma-32P]GTP was inhibited by captan to the same extent as overall RNA synthesis. The ratio of [3H]UTP incorporation to that of [gamma-32P]ATP or of [gamma-32P]GTP in control and captan-treated samples indicated that initiation was inhibited, but the length of RNA chains being synthesized was not altered by captan treatment. Limited-substrate assays in which re-initiation of RNA chains did not occur also showed that captan had no effect on the elongation reaction. Studies which measured the interaction of RNA polymerase with template DNA revealed that the binding of enzyme to DNA was inhibited by captan. Glycerol-gradient sedimentation of the captan-treated RNA polymerase indicated that the inhibition of the enzyme was irreversible and did not result in dissociation of its subunits. These data are consistent with a mechanism in which RNA polymerase activity was irreversibly altered by captan, resulting in an inability of the enzyme to bind to the template. This interaction was probably at the DNA-binding site on the polymerase and did not involve reaction of captan with the DNA template.
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PMID:Mechanism of inhibition of Escherichia coli RNA polymerase by captan. 617 15