Despite the fact that UL49.5 is one of the five evolutionarily conserved HSV-1 glycoproteins, little is known about its functional significance in HSV-1. So far, the only function of HSV-1 UL49.5 that has been reported is the regulation of membrane fusion events by supporting gM . In some herpesviruses of the Varicellovirus genus, which comprise bovine, equine, suid, canid, and felid herpesviruses, UL49.5 homologs have been shown to possess an additional function of inhibiting the MHC class I-restricted antigen presentation. UL49.5 has been shown to inhibit the transporter associated with antigen processing (TAP) and the antigenic peptide transport into the ER . However, each of the TAP inhibitors seem to utilize a distinct mechanism .