Alignment of NblR with various response regulators of two component signal transduction systems. (A) NblR. (B) sll0396 (putative response regulator in Synechocystis sp. strain PCC 6803). (C) CopR (copper-related response regulator from Pseudomonas syringae). (D) PhoB (phosphorus-related response regulator from E. coli). (E) SphR (PhoB homolog of Synechococcus sp. strain PCC 7942). (F) OmpR (osmolarity-related response regulator of E. coli). Identical and similar residues in at least two of the sequences are on a black or gray background, respectively. The threonine (T) to isoleucine (I) change at amino acid 156 and α-helical regions (α1, α2, α3) and β-sheets (β1, β2) close to the helix–turn–helix (H, T, H) of the predicted DNA binding site are indicated.