Structure and mapping of the gene encoding mouse high affinity FcγRI and chromosomal location of the human FcγRI gene

We describe the isolation and characterization of the gene encoding the mouse high affinity Fc receptor FcγRI. Using a mouse cDNA FcγRI probe four unique overlapping genomic clones were isolated and were found to encode the entire 9 kb of the mouse FcγRI gene. Sequence analysis of the gene showed that six exons account for the entire FcγRI cDNA sequences including the 5'- and 3'-untranslated sequences. The first and second exons encode the signal peptide; exons 3, 4, and 5 encode the extracellular Ig binding domains; and exon 6 encodes the transmembrane domain, the cytoplasmic region, and the entire 3'-untranslated sequence. This exon pattern is similar to FcγRIII and FcεRI but differs from the related FcγRII gene which contains 10 exons and encodes the b1 and b2 FcγRII. Southern blot analysis had shown that the mouse FcγRI gene is a single copy gene with no RFLP in inbred strains of mice, but analysis of an intersubspecies backcross of mice showed that unlike other mouse FcR genes which are on mouse chromosome 1 the locus encoding FcγRI, termed Fcg1, is located on chromosome 3. Interestingly, the Fcg1 locus is located near the end of a region with known linkage homology to human chromosome 1. Analysis of human x rodent somatic cell hybrid cell lines indicates that the human FCG1 locus encoding the human FcγRI maps to chromosome I and therefore possibly linked to other FcR genes on this chromosome. These results suggest that the linkage relationships among these genes in the human genome are not preserved in the mouse.