Genomic structure of PIR-B, the inhibitory member of the paired immunoglobulin-like receptor genes in mice

The genes encoding the murine paired immunoglobulin-like receptors PIR-A and PIR-B are members of a novel gene family which encode cell-surface receptors bearing immunoreceptor tyrosine based inhibitory motifs (ITIMs) and their non-inhibitory/activatory counterparts. PIR-A and PIR-B have highly homologous extracellular domains hut distinct trans membrane and cytoplasmic regions A charged arginine in the transmembrane region of PIR-A suggests its potential association with other trans membrane proteins to form a signal transducing unit. PIR-B, in contrast, has an uncharged transmembrane region and several ITIMs in its cytoplasmic tail. These characteristics suggest that PIR-A and PIR-B which are coordinately expressed by B cells and myeloid cells, serve counter-regulatory roles in humoral and inflammatory responses. In the present study we have determined the genomic structure of the single copy PIR-B gene. The gene consists of 15 exons and spans approximately 8 kilobases. The first exon contains the 5' untranslated region, the ATG translation start site, and approximately half of the leader peptide sequence. The remainder of the leader peptide sequence is encoded by exon 2. Exons 3-8 encode the six extracellular immunoglobulin-like domains and exons 9 and 10 code for the extracellular membrane proximal and transmembrane regions. The final five exons (exons 11-15) encode for the ITIM-bearing cytoplasmic tail and the 3' untranslated region. The intron/exon boundaries of PIR-B obey the GT-AG rule and are in phase I, with the notable exception of the three boundaries determined for ITIM-containing exons. A microsatellite composed of the trinucleotide repeat AAG in the intron between exons 9 and 10 provides a useful marker for studying population genetics.