Single Ig IL1 Related Receptor (SIGIRR)

The deduced 410-amino acid human protein, which is 82% identical to the mouse sequence and 23% identical to IL1R, has no signal peptide and contains a short 118-amino acid single immunoglobulin (Ig) extracellular domain with 4 potential N-glycosylation sites; a transmembrane region; and a 268-amino acid cytoplasmic tail with 4 IL1R-like signaling motifs. However, 2 changes in the regions conserved with IL1R (ser447 in IL1R replaced by cys222 in motif 3 of SIGIRR, and tyr536 in IL1R replaced by leu305 in motif 4 of SIGIRR) are predicted to abrogate signaling capabilities. Northern blot analysis revealed wide but differential expression of predominant 2.4- and 1.5-kb transcripts and minor 4.4- and 0.9-kb transcripts in all tissues tested.