The presentation of viral peptides by MHC class I molucules at a cell surface singnals CD8 T cells to kill the infected cell. Some viruses evade immunerecognition by producing proteins celled immunevasins, which prevent the appearance of peptide : MHC class I complexes on the infected cell (Fig. 6.7). Some immuoevasins block peptide entry into the endoplasmic reticulum by targeting the TAP transporter (Fig. 6.8, top panel). The herpes simplex virus produces the protein produces the protein ICP47, which binds to the cytosolic surface of TAP and prevents peptide from entering the transporter, whereas the US6 protein from human cytomegalovirus bind to the luminal face of TAP and prevents peptide being transported by inhibiting TAP ATPase activity. The UL49.5 protein from boving herpes virus inhibits TAP peptide transport by blocking conformational changes in TAP that are required for peptide translocation, and also by targeting TAP proteins for proteasomal degradation.