SNAP output for PDB entry 8i24 [SNAP web server]

PDB-id

8i24; SNAP-derived features in text and JSON formats; DNAproDB

Class

transcription

Method

cryo-EM (3.36 Å)

Summary

Clostridium thermocellum RNA polymerase transcription open complex with sigi6 and its promoter

Reference

Li J, Zhang H, Li D, Liu YJ, Bayer EA, Cui Q, Feng Y, Zhu P (2023): "Structure of the transcription open complex of distinct sigma I factors." Nat Commun, 14, 6455. doi: 10.1038/s41467-023-41796-4.

Abstract

Bacterial σ_I factors of the σ₇₀-family are widespread in Bacilli and Clostridia and are involved in the heat shock response, iron metabolism, virulence, and carbohydrate sensing. A multiplicity of σ_I paralogues in some cellulolytic bacteria have been shown to be responsible for the regulation of the cellulosome, a multienzyme complex that mediates efficient cellulose degradation. Here, we report two structures at 3.0 Å and 3.3 Å of two transcription open complexes formed by two σ_I factors, SigI1 and SigI6, respectively, from the thermophilic, cellulolytic bacterium, Clostridium thermocellum. These structures reveal a unique, hitherto-unknown recognition mode of bacterial transcriptional promoters, both with respect to domain organization and binding to promoter DNA. The key characteristics that determine the specificities of the σ_I paralogues were further revealed by comparison of the two structures. Consequently, the σ_I factors represent a distinct set of the σ₇₀-family σ factors, thus highlighting the diversity of bacterial transcription.