Chaperone protein that cooperates with UL148 to regulate the abundance of gH complexes in virion (PubMed:33889136, PubMed:26937030). First interactor of gH in the host endoplasmic reticulum, regulates the early folding steps of virion assembly. Then, UL148 is recruited and favors the binding of gL (PubMed:34011552). Interacts with gH (PubMed:26937030). Interacts with UL148 (PubMed:33889136, PubMed:34011552). First localizes to the cellular site of virus assembly and then inserts into the virion envelope. Highly glycosylated. Deletion causes infectivity defects of about 10-fold compared to wild-type virus and leads to reduced expression of both gH/gL complexes in virions. Belongs to the HHV-5 UL116 protein family.