Alignment of vertebrate Epo and EpoR Sequences highlights conserved functional residues. Amino acid sequence comparison of Epo (A) and EpoR (B) from various vertebrate species (see “Results” for percentage of identity and similarity). (A) ● marks cysteines known to be required for the formation of disulphide bridges in mammals; the cysteines near the N- and C- termini are essential for stability and function. Double black circles indicate conserved N- and O-linked glycosylation sites; double gray circles indicate a predicted N-linked glycosylation site. (B) Conserved cysteines in the extracellular domain, required for ligand binding, are indicated by ○; the WSXWS domain, box 1, and box 2 are demarcated by black boxes; and the transmembrane domain (240-262) is marked by a thick black line. The 5 residues that comprise the hydrophobic patch are shaded in blue. Murine phosphotyrosines (with the exception of Y343) are boxed in black and labeled according to the mouse EpoR sequence. Murine Y343 is shaded in red within a red box, believed to be a consensus site for STAT5 binding; putative STAT5 binding sites in fish and frog are likewise marked. Identical amino acids are shaded in dark gray; similar residues, in light gray. The signal peptide is depicted above the mature EpoR.