The GM-CSF receptor alpha subunit has a single transmembrane domain, a glycosylated extracellular domain and a short (54 amino acids) cytoplasmic tail, containing no tyrosine kinase domain (Gearing et al. 1989). It binds GM-CSF with a relatively low affinity, and is not capable of signaling. The cytoplasmic domain of the alpha chain appears to be critical for GM-CSF signaling (Matsuguchi et al. 1997).