Practice question

Among general Pol II factors, TFIIH alone possesses ATP-dependent DNA helicase activity essential for promoter opening. Complex composed of ten subunits includes XPB ERCC3 translocase with 3' to 5' helicase that pumps downstream DNA toward polymerase, generating torsional stress to melt eleven to fifteen base pairs around transcription start site. XPD ERCC2 helicase participates primarily in nucleotide excision repair. Helicase action requires ATP hydrolysis and is inhibited by triptolide anticancer drug. TFIIH entry after Pol II-TFIIF completes preinitiation complex assembly enabling open complex formation.