Novoblocin inhibits initiation of RNA potymerase Il-directed transcription of the moose metaDothiondn-I gene independent of its effect oo DNA topoisomerase II

Abstract
The requirement for ATP hydrolysis in the initiation of RNA polymerase II (Pol II)-directed transcription and the relationship between ATP and novobiocin action led us to Investigate whether novoblocin could inhibit transcription of the House netallothioneln-I (MT-I) gene. Novobiocin Inhibited the MT-I gene transcription in a fractionated rat hepatoma nuclear extract In a dose-dependent manner by direct interaction with a nuclear factor(s). This interaction prevented formation of stable prelnitlation complexes but did not affect elongation of MT-I mRNA. Preincubatlon of the nuclear extract with ATP prevented the action of novobiocin on MT-I gene transcription. Although novobiocin is known to Inhibit DNA topolsomerase II, VM-26, a specific inhibitor of this enzyme had no effect on the transcription. These results indicate that novobiocin blocks the Pol Il-directed transcription by Inhibiting formation of preinitiation complexes at an ATP-dependent step.