FIG. 6.

CTD phosphorylation using immunopurified proteins with antibodies to TFIIH subunits. (A) Antibodies to TFIIH subunits ERCC3 (p89) (αERCC3) and p62 (αp62) or to TBP (αTBP) were used for immunoprecipitation from the HeLa cell nuclear extract. These immunoprecipitates were then used in kinase assays to phosphorylate GST-CTD, resulting in ³²P-labeled GST-CTD_o and GST-CTD_a as indicated. Molecular mass markers (in kilodaltons) are indicated to the left. (B) Antibodies to TFIIH subunit p62, (αp62), cyclin H, (αcyclinH), or MO15 (cdk7) (αMO15) were used to immunopurify proteins from untreated (−) or cdc2-treated (+) HeLa cell nuclear extract. Kinase assays were performed with GST-CTD as a substrate.