The transmembrane domains of the γ chain and the α chains of FcγRI, FcγRIIIA, FcϵRI, and FcαRI. Indicated in bold are the following TM amino acids: cysteine Cys7 and aspartic acid Asp11 of the γ chain, aspartic acid Asp203 of FcγRIIIA, aspartic acid Asp195 of FcϵRI, asparagine Asn306 of FcγRI, and arginine Arg209 of FcαRI. The TMs of FcγRI, FcγRIIIA, and FcϵRI are aligned to display amino acid homologies.