Fig. 5

Recurrent mutations at galS and CRP-binding sites upstream of mglB. a Location and frequency of galS mutations on the primary structure. Circles represent alleles from chemostat 1, triangles represent alleles from chemostat 2, and squares represent alleles from chemostat 3. Synonymous mutations are colored green, missense mutations yellow, nonsense mutations red, and frameshift mutations blue. Scale bar (0–100) indicates frequency attained by a particular mutant in an experimental population. Gray shading indicates the GalS helix-turn-helix DNA-binding motif and stipple indicates the GalS ligand-binding domain. CRP-binding site mutations are not colored as they only alter DNA sequences. b Left: Ribbon diagram of dimeric E. coli purine repressor PurR bound to dsDNA. Three main functional regions of the protein are indicated: the N-terminal DNA-binding domain (orange), the C-terminal sub-domain involved in intramolecular signaling (blue), and the C-terminal sub-domain involved in dimer stabilization (green). The PurR ligand guanine is shown in gray cartoon style (PDBID 1WET) [67]. Middle: SWISSMODEL representation of the GalS repressor based on the structure of PurR (PDBID 1JFS, 32.53% sequence identity). Mutations grouped in the N-terminal DNA-binding domain are shown as orange spheres, while the two groups of C-terminal mutations indicated in a are shown in green and blue. Right: GalS model with conserved and repeatedly mutated residue Arg146 colored cyan and the remaining mutations that occurred in the middle portion of the protein colored purple