A role of the C-terminal part of p44 in the promoter escape activity of transcription factor IIH

The p44 subunit plays a crucial role in the overall activity of the transcr iption/DNA repair factor TFIIH: on the one hand its N-terminal domain inter acts with and regulates the XPD helicase (1, 2); on the other hand, as show n in the present study, it participates with the promoter escape reaction. Mutagenesis along with recombinant technology using the baculovirus/insect cells expression system allowed us to define the function of the two struct ural motifs of the C-terminal moiety of p44: mutations within the C4 zinc f inger motif (residues 291-308) prevent incorporation of the p62 subunit wit hin the core TFIIH. Double mutations in the RING finger motif (residues 345 -385) allow the synthesis of the first phosphodiester bond by RNA polymeras e II, but prevent its escape from the promoter. This highlights the role of transcription factor IIH in the various steps of the transcription initiat ion process.