O-77 - No close relative has a true S1-S2 insertion; RmYN02's reported insertion is only substitutions
The polybasic furin site and its PRRA insert are absent from all related lineage B betacoronaviruses; the RmYN02 virus reported to carry a natural PAA insertion at S1/S2 shows, on nucleotide alignment to its closest relatives (bat-SL-CoVZC45/ZXC21), only substitutions and no actual insertion.
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Why this is evidence
No close relative carrying a true S1/S2 insertion (RmYN02’s reported insertion is only substitutions) leaves the furin insertion without a natural template — favouring H-43; the natural members attribute the gap to undersampling.