TFIIH-mediated nucleotide excision repair and initiation of mRNA transcription in an optimized cell-free DNA repair and RNA transcription assay.

In mammalian cells, mRNA transcription is initiated with the aid of transcription initiation factors. Of these, TFIIH has also been shown to play an essential role in nucleotide excision repair (NER), which is a versatile biochemical pathway that corrects a broad range of DNA damage. Since the dual role of TFIIH is conserved among eukaryotes, including yeast and mammalian cells, the sharing of TFIIH between NER and RNA transcription initiation might provide some survival advantage. However, the functional relationship between NER and RNA transcription initiation through TFIIH is not yet understood. We have developed an optimized cell-free assay which allows us to analyze NER and RNA transcription under identical conditions. In this assay, NER did not compete with RNA transcription, probably because the extracts contained sufficient amounts of TFIIH to support both processes. Thus, NER can be considered functionally independent of RNA transcription initiation despite the fact that both processes use the same factor.