ジャーナル: Proc Natl Acad Sci U S A / 年: 2023 タイトル: An SI3-σ arch stabilizes cyanobacteria transcription initiation complex. 著者: Liqiang Shen / Giorgio Lai / Linlin You / Jing Shi / Xiaoxian Wu / Maria Puiu / Zhanxi Gu / Yu Feng / Yulia Yuzenkova / Yu Zhang / 要旨: Multisubunit RNA polymerases (RNAPs) associate with initiation factors (σ in bacteria) to start transcription. The σ factors are responsible for recognizing and unwinding promoter DNA in all ...Multisubunit RNA polymerases (RNAPs) associate with initiation factors (σ in bacteria) to start transcription. The σ factors are responsible for recognizing and unwinding promoter DNA in all bacterial RNAPs. Here, we report two cryo-EM structures of cyanobacterial transcription initiation complexes at near-atomic resolutions. The structures show that cyanobacterial RNAP forms an "SI3-σ" arch interaction between domain 2 of σ (σ) and sequence insertion 3 (SI3) in the mobile catalytic domain Trigger Loop (TL). The "SI3-σ" arch facilitates transcription initiation from promoters of different classes through sealing the main cleft and thereby stabilizing the RNAP-promoter DNA open complex. Disruption of the "SI3-σ" arch disturbs cyanobacteria growth and stress response. Our study reports the structure of cyanobacterial RNAP and a unique mechanism for its transcription initiation. Our data suggest functional plasticity of SI3 and provide the foundation for further research into cyanobacterial and chloroplast transcription.