Figure 1. The Crl binding region of S. Typhimurium σ^S and sequence comparison of σ^S from species harbouring crl or lacking crl.

(a) Cartoon representation of the structural model¹⁶ of full-length σ^S_STM, in which domains σ^S₂, σ^S₃ and σ^S₄ are shown. The helix α2¹⁶,²¹ and the DPE motif²¹ within σ^S₂ are highlighted. (b) Zoomed view of σ^S₂ in which the side chains of critical residues are depicted in cyan and yellow. (c) WebLogo (http://weblogo.threeplusone.com/create.cgi) of σ^S residues 71–91 (numbered as in σ^S_STM) generated with the σ^S sequences listed in Supplementary Figure S2, from bacterial genomes containing crl or lacking crl. (d) Sequence alignment of σ^S helix α2 from S. Typhimurium and P. aeruginosa, both with their own numbering. Residues that differ between σ^S_PA and σ^S_STM are highlighted in the alignment and represented with the same colour code as in the surface representation of S. Typhimurium σ^S₂ shown above.