WRAPPING OF PROMOTER DNA AROUND THE RNA-POLYMERASE-II INITIATION COMPLEX-INDUCED BY TFIIF

The formation of the RNA polymerase II (Pol II) initiation complex was analyzed using site-specific protein-DNA photo-cross-linking. We show that the RAP74 subunit of transcription factor (TF) IIF, through its RAP30-binding domain and an adjacent region necessary for the formatio n of homomeric interactions in vitro, dramatically alters the distribu tion of RAP30, TFIIE, and Pol II along promoter DNA between positions -40 and +26. This isomerization of the complex, which requires both TF IIF and TFIIE, is accompanied by tight wrapping of the promoter DNA fo r almost a full turn around Pol II. Addition of TFIIH enhances photo-c ross-linking of Pol II to a number of promoter positions, suggesting t hat TFIIH tightens the DNA wrap around the enzyme. We present a genera l model to describe transcription initiation.