MOLECULAR EVOLUTION OF THE C-TERMINAL CYTOPLASMIC DOMAIN OF A SUPERFAMILY OF BACTERIAL RECEPTORS INVOLVED IN TAXIS

Twenty-nine proteins from 16 different species of prokaryotes revealed an extensive sequence homology with the cytoplasmic domain of the Esc herichia coli aspartate receptor. The high percentage of identity indi cated that they constitute a superfamily of proteins. A consensus seco ndary structure consisting mostly of alpha-helices was predicted. The occurrence of a seven-residue repeat (a-b-c-d-e-f-g), in which both th e a and d residues were hydrophobic with few exceptions, provided addi tional evidence for a conserved alpha-helical conformation. Sequence a lignments, together with the predicted secondary structure, led to ide ntification of the boundaries for the functional units constituting th e cytoplasmic domain. Putative methylation sites were assigned for all the members of this superfamily. These proteins could be grouped into three classes based on the presence of 14-residue insertion/deletion regions found within both the signalling and the methylation functiona l units of the cytoplasmic domain. The gene coding for the C-terminal cytoplasmic domain of these proteins apparently evolved through gene d uplication from a common ancestor in which the four original 14-residu e insertion/deletion regions were deleted two by two during evolution. (C) 1996 Academic Press Limited