Fig. 1: Cryo-EM structure of the M. tuberculosis EσB octamer.
a Schematic representation of the M. tuberculosis σA and σB subunits with the structural domains σ1.1 in white, σ2 in dark red, σ3 and σ4 in gray. The subregions inside the σ domains are numbered. NCR, non-conserved region. The solved part of σB (residues 17–158) is indicated by a hatched rectangle. b 14% SDS-PAGE of the EσB sample for cryo-EM. c Representative cryo-EM image of the EσB sample. Experiment was repeated independently four times. Scale bar = 50 nm. Bottom, representative 2D class averages of monomers (M) and oligomers (O). d Cryo-EM map of the octamer (EσB)8 refined without imposing symmetry (C1 -map). RNAP protomers with well-defined density are in light green (protomer R1), sky blue (protomer R5), and khaki (protomer R8). The other protomers are in gray. e. 3D-model of the D4 symmetric octamer with the protomers numbered R1 to R8 and the symmetry axes indicated. Color codes are as in d. f Scatter chart shows volumes of the individual protomers in C1-map calculated in UCSF Chimera. g Molecular model of the octamer (EσB)8. Views from the top (protomers R1, R2, R3, R4) and from the side (protomers R2, R3, R7, R8) with the RNAP subunits color-coded as indicated on the left: yellow and orange α, cyan β, magenta β‘, dark red σB. The boxed region shows the junction between the top and bottom rings of RNAP tetramers (EσB)4. Domains holding the RNAP protomers together: β flap (aa 808–832, cyan), β‘ clamp (aa 1–413, magenta) and \({\sigma }_{2}^{{{{{{\rm{B}}}}}}}\) (dark red). The other regions are in gray. Source data are provided as a Source Data file.
