Binds and activates the KLRK1/NKG2D receptor, mediating natural killer cell cytotoxicity. Down-regulates the expression of KLRK1 and stimulates natural killer cells to secrete IFNG. Stimulates natural killer cells to secrete IFNG. Interacts with KLRK1/NKG2D. (Microbial infection) In CMV-infected cells, interacts with the viral glycoprotein UL16; this interaction causes RAET1G retention in the endoplasmic reticulum and cis-Golgi and prevents binding to and activation of KLRK1/NKG2D, providing CMV with an immune evasion mechanism. Mainly found intracellularly. Isoform 1 is highly expressed in colon and in a number of tumor cell lines and highly restricted in normal tissues. Both isoforms are frequently expressed in cell lines derived from epithelial cancers, and in primary breast cancers. The functional form is cleaved C-terminally of the GPI-anchor and yields a 28 kDa protein. UL16-binding proteins (ULBPs) are unusual members of the extended MHC class I superfamily. They do not contain the alpha 3 domain and lack a transmembrane domain. Belongs to the MHC class I family.