Fas Apoptotic Inhibitory Molecule 3 (FAIM3)

Fc receptors specifically bind to the Fc region of immunoglobulins (Igs) to mediate the unique functions of each Ig class. FAIM3 encodes an Fc receptor for IgM. The predicted 390-amino acid type I integral membrane protein has a signal peptide; an extracellular region homologous to immunoglobulin (Ig) variable domains, but with 2 additional cysteines; and a cytoplasmic region containing a basic region, an acidic region, and a proline-rich region. RNA dot blot analysis detected strong expression of TOSO in lymph node, lung, and kidney. Northern blot analysis detected a major 2.0-kb TOSO transcript, as well as minor transcripts of 2.8, 3.5, and 4.3 kb, in lymph node, spleen, peripheral blood leukocytes, and thymus. RT-PCR analysis detected TOSO expression in lymphoid cell lines, but not in nonhemopoietic cell lines.