Abstract
Our laboratory has been involved in the identification and characterization of the transcription factors for RNA polymerase I (Pol I)- directed transcription of ribosomal RNA genes (rDNA). To this end, we initially isolated and partially purified a transcriptionally active protein complex which contains RNA polymerase I and the essential Pol I transcription factors (1). Such a fraction was obtained from whole cell extracts (1) or from nuclear extracts (2). Subsequently, we demonstrated that a fraction obtained during chromatography of the cell extract on a heparin sepharose column could prevent nonrandom transcription of cloned rat rDNA in an in vitro system (3). The major protein in this fraction exhibited characteristics of purified poly(ADP-ribose) polymerase. The present report summarizes the properties of this protein, and describes experiments showing the dramatic appearance of accurately initiated transcript in an unfractionated whole cell extract or nuclear extract from a tissue following addition of the protein factor.
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