In 1971, microbiologists examining yeast cells discovered strange, rogue fragments of RNA that turned out to be viruses. These “narnaviruses” (a portmanteau of “naked RNA viruses”) had several odd properties. They were tiny — essentially a single gene encoding an enzyme that helped the virus make copies of itself. Moreover, unlike other single-stranded RNA viruses like Ebola and influenza, they had no “capsid” shell enclosing their genetic material, leaving them exposed and restricting them to their host cells.
Strangest of all, narnaviruses could be read backward…
The researchers observed that the opposing reading frames in ambigrammatic narnaviruses were always aligned, with codon boundaries perfectly matched up. They realized that this alignment allows stop codons to disappear from the reverse sequence over the course of evolution without ruining the replication enzyme encoded by the forward strand. That is, anytime a codon in the forward sequence leaves the reverse complement with a stop, the forward codon could in theory be replaced with a “synonym” codon that translates into the same amino acid, removing the stop on the reverse complement without repercussions.
That doesn’t work when the forward and reverse reading frames are staggered. For such a long overlap, “there’s really only one way you could ever do this … and the narnaviruses use that solution,” DeRisi said. “That in turn suggests that this is not a random boo-boo on evolution’s part.”Jordana Cepelewicz, “New clues about am bigram viruses with strange, reversible genes” at Quanta
“Not a random boo-boo on evolution’s part”? If the field of biology had not organized itself around Darwinian evolution (insert preferred terminology for the same sort of thing here) in the mid-twentieth century, would anyone think that up just now to account for all this?
Anyway, happy Evolution Weekend!
See also: What? A virus with no recognizable genes? From what they’re saying, viruses don’t necessarily share any characteristics of common descent. Let alone universal common descent. Jury’s still out but this is big.