O-76 - The PRRA furin-site insertion is out of frame relative to aligned RaTG13-MP789
Aligned against RaTG13 and pangolin MP789, the PRRA insertion is out of reading frame: it splits the original serine codon TCA into a new serine codon (TCT) plus part of an alanine codon (GCA).
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Why this is evidence
The out-of-frame PRRA insertion is read by the lab side as ruling out natural slippage-type insertion (favouring H-43) and by the natural side as what a designer would avoid (a clean in-frame insert). Discriminates H-43 from H-41/H-42, direction contested.