Structures of full-length and mutant G-CSFR introduced into WEHI-3B D⁺ and LGM-1 cells by electroporation. The mutant G-CSFRs are designated by the letters of the alphabet (A, B, C, D, E, and F) and their degrees of truncation from the C-terminus of the cytoplasmic domain are illustrated. The cytokine receptor superfamily homology regions (Box 1, Box 2, and Box 3) are represented by boxes, and the four tyrosine residues (Tyr⁷⁰³, Tyr⁷²⁸, Tyr⁷⁴³, and Tyr⁷⁶³) in the murine G-CSFR cytoplasmic domain are indicated by “Y.” Amino acids are denoted by aa.