STRUCTURE OF THE GENE FOR THE HUMAN MYELOID IGA FC RECEPTOR (CD89)

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.