FIG. 5.

Schematic representation of the EnvZ protein. The sequences corresponding to conserved regions in histidine kinase proteins (I, II, and III) (37) are indicated by solid boxes. Region I contains the conserved histidine residue (H243) (11, 36), region II contains the conserved asparagine (N347) (5), and region III has a conserved glycine-rich segment. This last region is represented by five residues that are especially conserved (DXGXG…GXG). Hydrophobic putative membrane-spanning sequences (TM1 and TM2) are indicated by hatched boxes. The LR (putative linker) region has been suggested to modulate the activity of EnvZ (27). Mutants in the envZ gene which produced an amino acid substitution in the EnvZ protein that provided insight into its function as an osmolarity sensor are indicated (black circles) (12, 13). Other residues that have been implicated in the overall mechanism of osmoregulation by EnvZ are also shown. Spontaneous mutants have been found clustered in regions LR, I, and III (references 7 and 11 and references therein). Below the schematic representation of EnvZ domains, amino acid differences between E. coli and S. typhi EnvZ proteins are shown; the numbers represent amino acid positions.