The formation of the PIC begins with the binding of the TATA-binding protein (TBP), a subunit of TFIID, to the TATA box within the promoter region. This event serves as a nucleation point for the subsequent recruitment of other GTFs and RNA polymerase II. The PIC positions RNA polymerase II at the start site of transcription, where it catalyzes the polymerization of ribonucleotides into RNA. The helicase activity of TFIIH also plays a catalytic role by unwinding the DNA, creating a transcription bubble that allows RNA polymerase II to access the DNA template.
