[Trombone12]

> I ask because there were released US NIH emails discussing a base sequence not close to any in natural sequences

If you are seriously asking, you'll have to be much more specific about which exact sequence is being alleged as impossible; there have simply been too many unsound claims about something mysterious in the initial isolates for me to be able to guess what particular claim you want disproven.

If it's the furin site specifically that's supposedly unnatural, then that's simply false, and you can easily find debunkings of this if you just search for "furin site debunk". As an example, here's a recent paper about a very similar furin site (parts of it being identical to the canonical covid-19 site) found in a corona virus from wild bats captured in 2021: https://www.sciencedirect.com/science/article/pii/S1995820X2... this is simply put explicit observation of this "unnatural feature" found in nature.