Figure 1.

Alignment of amino acid sequences of FcαRI (X54150) and bFcγ2R (Z37506). S1 exons are shown from the methionine initiation codons. Because the gene structure of bFcγ2R is unknown, intron–exon boundaries are shown only for FcαRI. Amino acids that link two FcαRI exons are underlined, and the exon designation is shown above the sequence. Note that exon-linking amino acids are conserved between FcαRI and bFcγ2R. The first 19 amino acids of both sequences are considered to represent NH₂-terminal signal peptides, which are removed before cell surface expression. Thus, glutamine (Q) 22 is proposed to be the first amino acid of both mature proteins and therefore is designated +1. Isoleucine (I) 50 is also underlined. Residues of bFcγ2R identical to those of FcαRI are designated (*), and gaps that have been inserted to line up the sequences are designated (–) (also see reference 7).