Late protein that plays a role in intracellular enveloped virus (IEV) transport to the cell surface on microtubules. Together with protein E2, forms a complex that interacts with host KLC2 (kinesin light chain isoform 2) to engage the kinesin-1 complex and thereby promote IEV trafficking. Interacts with protein A36. Interacts with protein E2. Associates with the membrane of IEV particles, but not intracellular mature virus (IMV), cell-associated enveloped virus (CEV) or EEV. Colocalizes with microtubules. Not glycosylated or contains very little carbohydrate. Belongs to the poxviridae F12 protein family.