Thiol protease that cleaves the RNA1 and RNA2 polyproteins. Replicates the viral genome. 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.