Gene mapping of the three subunits of the high affinity FcR for IgE to mouse chromosomes 1 and 19.

The high affinity receptor for IgE (Fc epsilon RI) is a tetrameric structure consisting of a single IgE-binding alpha subunit, a single beta subunit, and two disulfide-linked gamma subunits. The alpha subunit of Fc epsilon RI and most Fc receptors are homologous members of the Ig superfamily. By contrast, the beta and gamma subunits from Fc epsilon RI are not homologous to the Ig superfamily. The gamma-chains do share a region of high homology with the zeta-chain of the TCR. No homology has been found to date for beta with any published sequence. Here, we report that a single copy gene encodes Fc epsilon RI beta and that the locus for Fc epsilon RI beta is found on mouse chromosome 19, genetically linked to the Ly-1 (Ly-12) locus and in a region that also contains Ly-10 and Ly-44 (CD20). Homology comparisons among these molecules reveal limited regions of homology between Fc epsilon RI beta and Ly-44 (CD20) as well as other striking similarities: both molecules have four putative transmembrane segments and a probably topology where both amino- and carboxytermini protrude into the cytoplasm. In addition, we show that a single gene for FC epsilon RI gamma is found at the distal end of mouse chromosome 1, clustered in a region where Fc epsilon RI alpha has also been linked to Fc gamma RII. At least one of the two forms of Fc gamma RII has recently been shown to contain gamma subunits identical to the gamma subunits of Fc epsilon RI. The close association of the genes for Fc epsilon RI alpha, FC gamma RII, and their shared gamma subunits raises interesting implications regarding coordinate regulation of gene expression.