Mapping the Location of TFIIB Within the RNA Polymerase II Transcription Preinitiation Complex: a Model for the Structure of the PIC

Biochemical probes positioned on the surface of the general transcription factor TFIIB were used to probe the architecture of the RNA polymerase II (Pol II) transcription preinitiation complex (PIC). In PICs, the TFIIB linker and core domains are positioned over the central cleft and wall of Pol II. This positioning is not observed in the smaller Pol II-TFIIB complex. These results lead to a new model for the structure of the PIC, which agrees with most previously documented protein-DNA interactions within Pol II and archaea PICs. Specific interaction of the TFIIB core domain with Pol II positions and orients the promoter DNA over the Pol II central cleft, and TBP-DNA bending leads to bending of the promoter around the surface of Pol II. The TFIIF subunit Tfg1 was found in close proximity to the TFIIB B finger, linker, and core domains, suggesting that these two factors closely cooperate during initiation.