FIG 3 .

Correlation between the size of the side chain at position 228 and activity in PhoQ. (A) ClustalO primary sequence alignment of the HAMP domains from Af1503 (GenBank no. O28769), PhoQ (P23837, D0ZV89, and Q9I4F8), CpxA (P0AE82), EnvZ (P0AEJ4), NarX (P0AFA2), Tsr (P02942), Tar (P07017), Aer2 (Q9I6V6), and Aer (P50466). ST, S. Typhimurium; Ec, E. coli; Pa, P. aeruginosa. The residues represented in blue are at the equivalent position as A291 in Af1503. In red are the two glutamate residues conserved in PhoQ. (B) Alkaline phosphatase activity of PhoQ mutants with amino acid substitutions at position 228. Cultures were grown in N minimal medium supplemented with 10 mM MgCl₂ (high) or 10 µM MgCl₂ (low). All values are means and standard deviations and are representative of at least three independent trials.