Identity and similarity of δ1 to other known cytokine receptors.

(A) Alignment of the extracellular domains of δ1 and the mouse common γ receptor (γ_c). (B) Comparison of the sequences of various hematopoietic growth factor receptors. A match of the amino acid residue between δ1 and other receptors is indicated by “*” (identical) or “:” (similar). Previously defined regions of homology, termed homology box1 and 2, are shown. The box1 and box2 are short characteristic motifs found in the membrane-proximal regions of type 1 cytokine receptors.44The box1 motif is defined by the PXP motif (proline, X, proline) preceded by hydrophobic sequences. Box2 is defined as a cluster of hydrophobic amino acids harboring some negatively charged amino acids.