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. 1997 Feb 18;94(4):1453–1458. doi: 10.1073/pnas.94.4.1453

Figure 2.

Figure 2

(Upper) A schematic domain structure of TodS and its amino acid sequence characteristics. bZIP is characterized by the repeating heptad leucines (L) and the preceding charged (+) residues (17). (Lower) A comparison with eukaryotic Fos, Jun, and GCN4 bZIP sequences is shown; in TodS an invariant asparagine (N) found among eukaryotic bZIP proteins is replaced by a lysine (K), but a conserved cysteine (C) at position −11 from the first leucine is present. Sk1 and Sk2 are two histidine kinase domains characterized by the conserved amino acid blocks known as H (HE—PL), N (Q—N—NA), G1 (D-G-G), F (F-PF), and G2 (G-GLGL) as compiled by Parkinson and Kofoid (4). These conserved residues in TodS are underlined. Srg contains the conserved DDSK residues (in boldface type) characteristic of bacterial response regulators; the conserved Ser (S) is often replaced by a Thr (T) (18). Shown below the boldface residues, for comparison, are the corresponding regions from the TodT sequence. The large asterisks indicate potential phosphorylation sites. The Sos domain is defined by amino acid sequence similarity with the oxygen-sensing domain of Rhizobium meliloti FixL (19) and related proteins from Azorhizobium caulinodans (AcORF1) (20). Invariant residues are underlined; cons, consensus residues. The top three similarity scores as defined by the blast program (ref. 21; National Center for Biotechnology Information, Bethesda) for the Sk1 domain are: ORFX18 and PhoR of Bacillus subtilis (GenBank accession nos. L09228L09228 and M23549M23549, respectively); CpxA of E. coli [Protein Identification Resource (PIR) no. A29549A29549]; for Sk2: NodV and NswA of Bradyrhizobium japonicum (GenBank accession nos. M31765M31765 and Z22637Z22637, respectively); C4-dicarboxylate sensor kinase of Rhodobacter capsulatus (PIR no. S30288S30288); for Srg: PhoB of R. meliloti (GenBank accession no. M96261M96261), phosphate acceptor regulatory protein (CheY) of P. aeruginosa (GenBank accession no. X61231X61231), and PhoB of Klebsiella pneumoneae (GenBank accession no. M31794M31794).