Picornain 3C-like protease is a thiol protease that probably cleaves the B and M polyproteins. Viral genome-linked protein (VPg) plays a role in RNA replication. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Specific enzymatic cleavages by picornain 3C-like protease in vivo yield mature proteins. Picornain 3C-like protease is autocatalytically processed (By similarity). Viral genome-linked protein (VPg) is uridylylated by the polymerase and is covalently linked to the 5'-end of genomic RNA. This uridylylated form acts as a nucleotide-peptide primer for the polymerase (By similarity). Belongs to the comoviridae genome polyprotein B family.