TFIIH generates a six-base-pair open complex during RNAP II transcription initiation and start-site scanning.

Tomko E.J., Fishburn J., Hahn S., and Galburt E.A.
TFIIH generates a six-base-pair open complex during RNAP II transcription initiation and start-site scanning.
Nat Struct Mol Biol. doi: 10.1038/nsmb.3500. (2017) (Abstract)