The +1 nucleosome functions in Pol II transcription initiation and the transition to elongation

Transcription initiation by RNA polymerase II (Pol II) occurs next to a +1 nucleosome that is positioned downstream of the transcription start site (TSS). The +1 nucleosome has been shown to influence the pre-initiation complex (PIC) assembly and Pol II pausing, but it is unclear whether and how it functions in transcription initiation and the transition to elongation. Here, we investigate the transcription initiation-elongation transition in vitro using DNA templates containing a +1 nucleosome, and we present cryo-EM structures of five intermediate states. First, after PIC assembly, the +1 nucleosome evicts TFIID from the PIC upon binding of ATP to TFIIH. Second, after DNA opening, the +1 n