Schematic of the GFP-Us9 protein and critical residues.

The topology and location of Green Fluorescent Protein amino-terminal fusion and the position of the critical and conserved acidic domain is presented. The majority of Us9 resides on the cytosolic side of the intracellular membrane, whereas a short carboxy terminal tail extends into the lumen of the vesicle. The acidic domain cluster resides just inside the transmembrane domain is highly conserved across alphaherpes virus species. For PRV Us9, the conserved tyrosines are critical for supporting anterograde transport and spread of virions. The serines located at positions 51 and 53 are highlighted, along with the conservation across alphaherpes viruses. The putative CK2 recognition sites delineated for each serine.