Replicase polyprotein contains helicase, VPg, protease and RNA-directed RNA polymerase functions. RNA-directed RNA polymerase replicates genomic and antigenomic RNA and transcribes the vial genome. The protease generates mature viral proteins from the precursor polyprotein. VPg is covalently linked to the 5'-end of genomic RNA. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) Specific enzymatic cleavages in vivo by the viral protease yield a variety of precursors and mature proteins.