Moreover, we compared the conservation of the two CTSL cleavage sites among seven known human CoVs and found that these CTSL cleavage sites exist only in SARS-CoV-1 and SARS-CoV-2 (Supplementary Fig. S2b), suggesting that CTSL would play a unique role in the process of SARS-CoV-1/2 infection. This evidence concerns the gene CTSL and infection.