Schematic representation of G-CSF-R proteins studied. Cytoplasmic domains of wild-type and mutant receptors are shown. Boxes B1 and B2 denote subdomains conserved in members of the hematopoietin receptor superfamily, whereas Box B3 is conserved only with a limited number of family members, including gp130.62 63 Y, tyrosine; F, phenylalanine; L, leucine; A, alanine.