The function of this internally encoded 3CLpro is integral to the processing of these proteins and critical for viral replication.7 The SARS CoV-1 3CLpro shares a high degree of structural homology and similar substrate specificity with the coronavirus 3C-like cysteine proteases of hCoV 229E and TGEV8 but is most similar to the SARS CoV-2 3CLpro.