Construction of the EGF receptor/EPO receptor chimera EECA-Y429, 431DF, and confirmation of its enhanced mitogenic activity in myeloid FDC2 cells. (A) For use in experiments designed to determine the effect of HCP recruitment in ligand-mediated SKT6 cell hemoglobinization, two EGF receptor/EPO receptor chimeras were constructed, EECA and EECA-Y429, 431F. In EECA, the extracellular domain is that of the human EGF receptor, and the transmembrane and cytoplasmic domains are those of the murine EPO receptor. In EECA-Y429, 431F, codons for tyrosine residues 429 and 431 of EECA are mutated to encode phenylalanine. (B) To confirm and to initially compare the activities of the above EECA and EECA-Y429, 431F chimeric receptors, constructs were expressed stably in myeloid FDC2 cells and their abilities to mediate mitogenesis were assayed based on rates of EGF-stimulated [methyl-³H] thymidine incorporation. Values are means (±standard deviations) for triplicate cultures.