ULBP-3 is a member of a family of cell-surface proteins that function as ligands for human NKG2D. ULBP-3 has also been described under the names RaeT1N (retinoic acid early transcript), NKG2DL3, and ALCAN-gamma. The name ULBP-3 derives from the original identification of three proteins, ULBP-1, -2, and -3, as ligands for the human cytomegalovirus glycoprotein UL16; they were designated UL16 binding proteins (ULBP). The gene for ULBP-3 resides in a cluster of ten related genes, six of which encode potentially functional glycoproteins. Amino acid sequence identity within this family ranges from 30-60%. These proteins are distantly related to MHC class I proteins, but they possess only the alpha 1 and alpha 2 Ig-like domains, and they have no capacity to bind peptide or interact with beta 2-microglobulin. Some family members, including ULBP-3, are anchored to the membrane via a GPI-linkage, whereas others have transmembrane domains.