Binds and activates the KLRK1/NKG2D receptor, mediating natural killer cell cytotoxicity. Binds to KLRK1/NKG2D. (Microbial infection) Contrary to other family members, does not interact with CMV glycoprotein UL16. Predominantly expressed in the skin, but also expressed in testis and trachea. Up-regulated in tumor cells of different origins. Expression progressively decreased after treatment of tumor cells with retinoic acid. MHC class I alpha-1 like and MHC class I alpha- like regions down-regulate the cell surface expression of KLRK1. 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. Contrary to other family members, does not interact with CMV glycoprotein UL16.