Picornain 3C-like protease is a thiol protease that cleaves the P1 and P2 polyproteins. 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). 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 nepoviruses RNA1 polyprotein family.