Pre Initiation Complex

In eukaryotic gene expression the Pre Initiation Complex (PIC) mediates the binding between the genome's promoter and RNA polymerase. Each type of RNA polymerase has a different PIC .

Subunits

The complexicity of PIC varies between the types of eukaryotic RNA polymerase. For polymerases I and III the complex consists of only a few subunits.

For polymerase II the PIC is far more complex. It consists of 6 General Transcription Factors (GTF). TFIID is the core recognition protein and binds to the TATA box. TFIIA stabilizes the binding complex. TFIID intreacts with TFIIB which brings in the RNA polymerase II which has TFIIF attached to it. This allows TFIIE and finally TFIIH to bind. TFIIH has helicase activity and starts seperating the strands at the Open Complex, this process requires ATP-hydrolysis. Further it has CTD Kinase activity and facilitates DNA repair.