O-74 - SARS-CoV-2 has a RaTG13-like backbone but a pangolin-CoV-like RBD (chimeric structure)
SARS-CoV-2 is ~96.2% identical genome-wide to bat CoV RaTG13 (its closest full-genome relative) and 79% to SARS-CoV, yet its RBD is nearly identical to the pangolin coronavirus MP789: SARS-CoV-2 and pangolin CoV share identical amino acids at the five critical RBD contact residues while RaTG13 shares only one - a chimeric backbone-vs-RBD split.
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Why this is evidence
A RaTG13-like backbone carrying a pangolin-like RBD is read as a laboratory chimera (favouring H-43); the natural members explain the same backbone/RBD split by recombination (O-73). Discriminates H-43 from H-41/H-42, direction contested.