Schematic representation of mutant EpoRs. Mutant EpoRs employed are schematically shown along with the wild-type EpoR and EGFR. The membrane-proximal cytoplasmic domain of EpoR containing the Box 1 and Box 2 sequences is represented by a striped box. Thick horizontal lines represent tyrosine residues in the EpoR cytoplasmic region. The four conserved cysteine residues in the EpoR extracellular domain are represented by thin horizontal lines. Numbers in parentheses denote the carboxy-terminal amino-acid numbers. Abbreviations used are: WSXWS, the WSXWS motif; W282R, the mutation of Trp²⁸² to Arg; CRD, the cysteine-rich domain; TKD, the tyrosine kinase domain.