A better understanding of IgA's role in immunity requires insight in I
gAR complexity. We have now isolated, characterized, and sequenced the
gene encoding the prototypic human myeloid IgA FcR (CD89), The gene c
onsists of five exons and spans approximately 12 kilobase pairs. The l
eader peptide is encoded by two exons, the second of which is 36 bp lo
ng and specifies the predicted peptidase cleavage site. A similar, but
shorter (21 bp) mini-exon has been found in the FcR for IgG (Fc gamma
R) genes, and the FcR for IgE (Fc epsilon Rl alpha) gene (human and r
odent), The third and fourth exons code for two homologous Ig-like dom
ains. The final exon encodes a short extracellular region, a hydrophob
ic transmembrane region, and a short cytoplasmic tail, The sequence of
the 5'-flanking region was determined, and one major and several mino
r transcription initiation sites were mapped by primer extension studi
es, A putative TATA box was located at an appropriate location relativ
e to the start site, Southern blot analyses of genomic DNA confirm the
restriction map generated from cloned DNA. These data define the Fc a
lpha R gene as a distantly related member of the IgR gene family.