For example, the presence of a polybasic (RRAR) site at the S1/S2 cleavage site found in SARS-CoV-2, but not in other βCoVs in lineage B, which is cleaved by furin pre-activating the viral S proteins during virus exit, reduces dependence of the viral S proteins on target cell proteases for virus entry and thus facilitates the virus infection [245]. Here, PROS1 is linked to viral infectious disease.