Participates in the inhibition of the host immune response. Redirects newly synthesized major histocompatibility complex (MHC) class I heavy chains via the SEC61 translocon to the cytosol where they undergo proteasome-dependent destruction. In consequence, infected cells are masked for immune recognition by cytotoxic T-lymphocytes. Interacts with host TRAM1. Expressed at early and late period of virus infection. N-glycosylated. A fraction of newly synthesized molecules retain the signal peptide after the N-linked glycan has been attached and translation of the polypeptide has been completed. Delayed cleavage of the signal peptide is determined by the first four residues, as well as by the transmembrane region (By similarity). Belongs to the cytomegalovirus US6 family.