VPg

VPg (viral protein genome-linked) is a protein that is covalently attached to the 5′ end of positive strand viral RNA and acts as a primer during RNA synthesis in a variety of virus families including Picornaviridae and Caliciviridae. The primer activity of VPg occurs when the protein becomes uridylylated, providing a free hydroxyl that can be extended by the virally encoded RNA-dependent RNA polymerase. Aside from functioning as a primer, VPg also has a role in translation initiation by acting like a 5' mRNA cap.