sentences:  Ligand binding to either subunit is required for and precedes dimerization and activation of the receptor.Each subunit of IFNAR contains an N-terminal ligand binding domain (with two or four fibronectin type II-like subdomains, for IFNAR2 and IFNAR1, respectively), a transmembrane (TM) domain, and a cytoplasmic domain.Each type I IFN ligand contains a "hotspot", or a sequence of conserved amino acids that are involved in binding to the receptor, specifically the high affinity receptor IFNAR2, which determines the affinity of each ligand for the receptor.