UL16 Binding Brotein 1 (ULBP1)

Sequence analysis predicted that the 242-amino acid protein, which is 60% and 55% identical to ULBP2 and ULBP3, respectively, contains alpha-1 and alpha-2 domains, like MICA, MICB, and HLA-A , but lacks the alpha-3 domain involved in the association of these molecules with beta-2-microglobulin (B2M. Instead of a transmembrane domain, ULBP1 has a putative glycosylphosphatidylinositol (GPI) linkage to the membrane. Enzymatic analysis confirmed that the ULBPs are indeed GPI-linked at the cell surface. RT-PCR analysis detected ULBP expression in T, B, and erythroleukemia cell lines and in a wide range of tissues. Expression was upregulated in colon and stomach tumors and downregulated in kidney tumors. FACS analysis demonstrated that protein expression generally correlated with message expression.