TFIIHc
TFIIH is a large, multi-subunit transcription factor that plays a crucial role in the initiation and promoter clearance phases of eukaryotic transcription by RNA polymerase II. It is a key component of the general transcription factor (GTF) machinery, acting at the pre-initiation complex (PIC) assembly stage. TFIIH possesses two distinct subcomplexes: a core complex and a transcription/DNA repair module. The core complex, consisting of XPB, XPD, and p44 subunits, is responsible for the ATP-dependent unwinding of the DNA double helix at the transcription start site. XPB is a DNA helicase that unwinds the DNA, while XPD is another helicase that also possesses 3'-5' exonuclease activity.
The transcription/DNA repair module, also known as the cyclin-dependent kinase (CDK)-activating kinase (CAK) module, comprises CDK7,