Gene structures of the α subunits of human IL-3 and granulocyte-macrophage colony-stimulating factor receptors: Comparison with the cytokine receptor superfamily

Recently, many genes encoding the members of the cytokine receptor superfamily (CRSF), which have common structural features, have been characterized. Analyses on the structures of the genes encoding the α subunits of human IL-3 (hIL-3Rα) and granulocyte-macrophage colony-stimulating factor receptors (hGMRα) revealed that they have the structural features common to all members of the CRSF (i.e., conservation of the intron phase pattern as "1-2-1-0-1" rule in the fibronectin type III domains located in extracellular segments of type I cytokine receptor subunits. This finding led us to propose a possible model for gene evolution for the CRSF. We pointed out that the CRSF genes derived from a putative common ancestral gene. In addition to these common features, we found an additional intron that is unique to the IL-3Rα and the GMRα genes. This additional intron suggests that the IL-3Rα and the GMRα genes evolved closely in the evolution process of the CRSF genes. This evidence and results of recent studies on the evolution of mammalian X chromosome make it tempting to speculate that a putative common ancestral gene of the subfamily including IL-3Rα, GMRα, and IL-5Rα emerged in an autosome at least before the divergence of marsupials and eutherian mammals, early in the 200 million-year history of mammals. (J ALLERGY CLIN IMMUNOL 1995;96:1115-25.).