Cysteine protease that generates mature viral proteins from the precursor polyprotein. In addition to its proteolytic activity, it binds to viral RNA, and thus influences viral genome replication. RNA and substrate cooperatively bind to the protease. Cleaves host PABP1, this cleavage is important for viral replication. Cleaves host TANK and disrupts the TANK-TBK1-IKKepsilon-IRF3 complex, thereby inhibiting the induction of the IFN-beta signal pathway 