Figure 5.

An alternative model for the assembly of a PIC. These models are different from the conventional stepwise assembly pathway in which TFIIE together with TFIIH are the last basal factors to enter the PIC. (A) TFIIE participates in the initial binding of TBP/TFIID to the promoter before the recruitment of the RNA pol II/TFIIF complex and TFIIH. It is pertinent to note that a role of TFIIE during the first steps of PIC assembly does not preclude a role during TFIIH recruitment (see Discussion). (B) To recruit TFIIH, TFIIE may either shift to alternate positions within the PIC or may contact both TBP/TFIIA and TFIIH at the same time, possibly accompanied by conformational changes of DNA upon PIC assembly (e.g., DNA bending by TBP/TFIID). This model illustrates the potential dual role of TFIIE in PIC formation and does not attempt to accommodate distinct RNA pol II complexes that have been described.