ISOLATION AND CHARACTERIZATION OF 2 HUMAN TRANSCRIPTION FACTOR IIH (TFIIH)-RELATED COMPLEXES - ERCC2 CAK AND TFIIH/

Transcription factor IIH (TFIIH) is a multisubunit protein complex ess ential for both the initiation of RNA polymerase class II (pol II)-cat alyzed transcription and nucleotide excision repair of DNA. Recent stu dies have shown that TFIIH copurifies with the cyclin-dependent kinase (cdk)-activating kinase complex (CAK) that includes cdk7, cyclin H, a nd p36/MAT1. Here we report the isolation of two TFIIH-related complex es: TFIIH and ERCC2/CAK. TFIIH* consists of a subset of the TFIIH com plex proteins including ERCC2 (XPD), p62, p44, p41, and p34 but is dev oid of detectable levels of ERCC2 (XPD) and CAK. ERCC2/CAK was isolate d as a complex that exhibits CAK activity that cosediments with the th ree CAK components (cdk7, cyclin H, and p36/MAT1) as well as the ERCC2 (XPD) protein, TFIIH can support pol II-catalyzed transcription in v itro with lower efficiency compared with TFIIH. This TFIIH-dependent transcription reaction was stimulated by ERCC2/CAK. The ERCC2/CAK and TFIIH complexes are each active in DNA repair as shown by their abili ty to complement extracts prepared from ERCC2 (XPD)- and ERCC3 (XPB)-d eficient cells, respectively, in supporting the excision of DNA contai ning a cholesterol lesion. These data suggest that TFIIH and ERCC2/CA K interact to form the TFIIH holoenzyme capable of efficiently assembl ing the pol II transcription initiation complex and directly participa ting in excision repair reactions.