Late protein that plays a role in intracellular enveloped virus (IEV) transport to the cell surface on microtubules. When absent, viral morphogenesis halts after the formation of IEV particles, and these are not transported to the cell periphery. Important for plaque formation, extracellular envelope virus (EEV) production and virulence (By similarity). Associates with the membrane of IEV particles, but not intracellular mature virus (IMV), cell-associated enveloped virus (CEV) or EEV. Colocalizes with microtubules (By similarity). Not glycosylated or contains very little carbohydrate. Belongs to the poxviridae F12 protein family.