Fig. 1. Sequence and structure of connexin polypeptides. (A) Amino-acid sequence alignment of human (h) and ß connexins and their mouse (m) homologues. Four positions (P1 to P4, boxed) at which the physico-chemical properties of amino-acid residues in all considered connexins drastically differed from all considered ß connexins were identified. P1 and P2 are located next to each other in the N-terminal region and P3 and P4 at the cytoplasmic end of TM3. The connexin (Cx) molecular weight nomenclature was used. (B) Topological model of Cx43. The four trans-membrane spanning helices (TM1 to TM4), the two extracellular loops (Loop 1, Loop 2), the intracellular loop and the N- and C-terminal domains are indicated. Asterisks indicate the four positions where -type specific amino-acid residues were replaced with corresponding residues of the ß-connexin, Cx32.