Picornain 3C-like protease is a thiol protease that probably cleaves the polyprotein. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Specific enzymatic cleavages by picornain 3C-like protease in vivo yield mature proteins (By similarity). Picornain 3C-like protease is autocatalytically processed. The Vt6 strain is a highly virulent strain.