TFIIH is a critical component of the pre-initiation complex (PIC) that facilitates the unwinding of DNA at the promoter region to allow RNA polymerase II to access the template strand. It contains two helicase subunits, XPB and XPD, which are responsible for the ATP-dependent unwinding of DNA. This unwinding is a form of catalysis, where the energy from ATP hydrolysis is used to drive a chemical reaction—in this case, the separation of DNA strands.
