(Top) The N-terminal transmembrane domain of ArcB was predicted with PHD htm program. A putative leucine zipper (2) was predicted on the basis of amino acid sequence homology. The primary transmitter domain (H1) contains the conserved His126 and the catalytic determinants N, G1, and G2. The G1 and G2 sequences typify nucleotide-binding motifs. The receiver domain (D1) contains the conserved Asp405, and the secondary transmitter domain (H2) of ArcB' contains the conserved His37 (3) (6).
(Bottom) ArcA consists of an N-terminal receiver domain (D2) containing the conserved Asp54 and a C-terminal helix-turn-helix (HTH) domain (4).
* This figure was modified from Kwon, O (5).