Reconstitution of +1 nucleosome transcription reveals coordinated functions of SAGA, Mediator, and TFIIH
- 1Stanford University School of Medicine
Abstract
The +1 nucleosome has emerged as a key regulator of eukaryotic transcription, but how it controls transcription initiation remains poorly understood. Here we reconstitute transcription through the +1 nucleosome using eleven purified yeast factors: RNA polymerase II (Pol II), the six general transcription factors (GTFs), TFIIS, the activator Pho4, and the SAGA and Mediator complexes. The system recapitulates key features of regulation observed in vivo. SAGA, acting with Pho4, directs pre-initiation complex (PIC) assembly to the correct position through its TBP-loading activity. Mediator stimulates transcription when the +1 nucleosome imposes a barrier to PIC formation, consistent with stabilization of productive TFIIH-DNA engagement. Contrary to the prevailing model, SAGA remains bound to the PIC after TBP loading and acetylates the +1 nucleosome within the assembled complex. The isolated PIC-Mediator-SAGA-nucleosome complex is transcriptionally active, and the repressive effect of the nucleosome is relieved by the DNA translocase activity of Ssl2, the TFIIH subunit that opens promoter DNA. TFIIH thus couples promoter melting to remodeling of the +1 nucleosome.
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BibTeX
@misc{nagai2026reconstitution,
title = {{Reconstitution of +1 nucleosome transcription reveals coordinated functions of SAGA, Mediator, and TFIIH}},
author = {S. Nagai and D.-H. Chen and R. U. H. Mattoo and H. Zhang and R. D. Kornberg},
howpublished = {bioRxiv},
year = {2026},
month = sep,
doi = {10.64898/2026.09.24.754195},
url = {https://www.biorxiv.org/content/10.64898/2026.09.24.754195v1},
note = {CC BY-NC},
}
RIS
TY - UNPB
TI - Reconstitution of +1 nucleosome transcription reveals coordinated functions of SAGA, Mediator, and TFIIH
AU - S. Nagai
AU - D.-H. Chen
AU - R. U. H. Mattoo
AU - H. Zhang
AU - R. D. Kornberg
PY - 2026
DA - 2026/09/24
PB - bioRxiv
DO - 10.64898/2026.09.24.754195
UR - https://www.biorxiv.org/content/10.64898/2026.09.24.754195v1
AB - The +1 nucleosome has emerged as a key regulator of eukaryotic transcription, but how it controls transcription initiation remains poorly understood. Here we reconstitute transcription through the +1 nucleosome using eleven purified yeast factors: RNA polymerase II (Pol II), the six general transcription factors (GTFs), TFIIS, the activator Pho4, and the SAGA and Mediator complexes. The system recapitulates key features of regulation observed in vivo. SAGA, acting with Pho4, directs pre-initiation complex (PIC) assembly to the correct position through its TBP-loading activity. Mediator stimulates transcription when the +1 nucleosome imposes a barrier to PIC formation, consistent with stabilization of productive TFIIH-DNA engagement. Contrary to the prevailing model, SAGA remains bound to the PIC after TBP loading and acetylates the +1 nucleosome within the assembled complex. The isolated PIC-Mediator-SAGA-nucleosome complex is transcriptionally active, and the repressive effect of the nucleosome is relieved by the DNA translocase activity of Ssl2, the TFIIH subunit that opens promoter DNA. TFIIH thus couples promoter melting to remodeling of the +1 nucleosome.
ER -