Sequence analysis of SARS-CoV-2 S reveals the presence of a four amino acid residue insertion at the boundary between S1 and S2 subunits compared with SARS-CoV S  and SARSr-CoV S. This results in the introduction of a furin cleavage site, a feature conserved among the 144 SARS-CoV-2 isolates sequenced to date but not in the closely related RaTG13 S.