SEQUENCE-SPECIFIC TRANSACTIVATORS COUNTERACT TOPOISOMERASE-II-MEDIATED INHIBITION OF IN-VITRO TRANSCRIPTION BY RNA POLYMERASE-I AND POLYMERASE-II

An inhibitor of RNA polymerase II transcription in vitro has been puri fied from HeLa cell nuclear extracts. Partial amino acid sequences der ived from the purified protein revealed that the inhibitor of transcri ption corresponded to human topoisomerase II. Order of addition experi ments provided evidence indicating that topoisomerase II inhibited tra nscription by binding over the core promoter and blocking preinitiatio n complex formation. Topoisomerase II-mediated repression could be rel ieved by sequence-specific transcriptional activators, having differen t activating and/or DNA binding domains, but antirepression required a transcriptional activation function in addition to a DNA binding doma in. Moreover, transcription by RNA polymerase I was also inhibited by topoisomerase II and this inhibition could be relieved by the RNA poly merase I transactivator UBF. These observations suggest that topoisome rase II may participate in a general repression of transcription which can be counteracted by transcriptional activators.