Displays RNA helix destabilizing and strand annealing acceleration activity. This activity is necessary at several points during genome replication, for example to separate duplexes that form after genome replication. Cysteine protease that generates mature viral proteins from the precursor polyprotein. Replicates genomic and antigenomic RNA. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) ATP + H2O = ADP + H(+) + phosphate Optimum pH is 7.5 for 3C-like protease. Optimum temperature is 22 degrees Celsius. Specific enzymatic cleavages in vivo by the viral 3C-like protease yield three mature proteins.