Structure of mutant G-CSFR proteins. The extracellular (ED), transmembrane (TM), and cytoplasmic domain (CD) of the murine G-CSFR are shown. The position of tyrosine residues (Y) in the cytoplasmic domain also are shown. The d716 construct contains a point mutation at nucleotide 2403 of the murine cDNA that introduces a premature stop codon resulting in the truncation of the G-CSFR at amino-acid 716. The GEpoR mutation represents an in frame fusion of the extracellular, transmembrane, and first four amino acids of the cytoplasmic domain of the murine G-CSFR with the cytoplasmic domain of the murine erythropoietin receptor.