Fig. 1
From: Structural basis of ECF-σ-factor-dependent transcription initiation
Structures of group-1 and ECF σ factors. a Structural organization of group-1 (σA) and ECF (σL) σ factors. Conserved regions σR1.1, σR1.2, σR2, σR3, σR3/4 linker, and σR4 are in light orange, dark orange, yellow, green, dark green, and cyan, respectively. Dashed line, non-conserved σR2/4 linker present in ECF σ factors. b Crystal structures of group-1 (Mtb RPitc-σA; PDB 5UH8) and ECF (Mtb RPitc-σL; PDB 6DVC) transcription initiation complexes (two orthogonal views of each). σ factors are shown in tube representations with conserved regions colored as in (a). Gray ribbon, RNAP core enzyme; blue, pink, red, and magenta ribbons, -10 element of DNA nontemplate strand, rest of DNA nontemplate strand, DNA template strand, and RNA product; violet sphere, RNAP active-center Mg2+. Other colors are as in (a). See Supplementary Figs. 1, 2, and 7
