Thiol protease that cleaves the RNA1 and RNA2 polyproteins. Plays a role in RNA replication. It is covalently linked to the 5'terminus of both viral single-stranded RNA1 and RNA2 molecules. Down-regulates the RNA1 polyprotein processing and enhances trans-cleavage of RNA2 polyproteins. The protease cofactor and the putative helicase seem to target the replication complexes to ER membranes. Their physical association causes the membrane rearrangement of host ER that may result in formation of the small membranous vesicles that are the site of viral RNA synthesis. The protease cofactor and the putative helicase seem to target the replication complexes to ER membranes. Their physical association causes the membrane rearrangement of host ER that may result in formation of the small membranous vesicles that are the site of viral RNA synthesis. Replicates the viral genome. a ribonucleoside 5'-triphosphate + RNA(n) = diphosphate + RNA(n+1) RNA1 polyprotein: Specific enzymatic cleavages by picornain 3C-like protease in vivo yield mature proteins. Picornain 3C-like protease is autocatalytically processed. 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.