Rapid switching of TFIIH between RNA polymerase I and II transcription and DNA repair in vivo.

The transcription/repair factor TFIIH operates as a DNA helix opener in RNA polymerase II (RNAP2) transcription and nucleotide excision repair. To study TFIIH in vivo, we generated cell lines expressing functional GFP-tagged TFIIH. TFIIH was homogeneously distributed throughout the nucleus with nucleolar accumulations. We provide in vivo evidence for involvement of TFIIH in RNA polymerase I (RNAP1) transcription. Photobleaching revealed that TFIIH moves freely and gets engaged in RNAP1 and RNAP2 transcription for approximately 25 and approximately 6 s, respectively. TFIIH readily switches between transcription and repair sites (where it is immobilized for approximately 4 min) without large-scale alterations in composition. Our findings support a model of diffusion and random collision of individual components that permits a quick and versatile response to changing conditions.