Transcription Factor II H

TFIIH is one of several general transcription factors that make up the RNA polymerase II preinitiation complex. TFIIH contains a number of subunits with different functions. Two of the subunits, ERCC2/XPD and ERCC3/XPB, have helicase activity and help create the transcription bubble. In a test tube these subunits are only required for transcription if the DNA template is not already denatured or supercoiled. Two other TFIIH subunits, CDK7 and cyclin H, phosphorylate serine amino acids on the RNA polymerase II C-terminal domain and possibly other proteins involved in the cell cycle.