There's 6-base pair organisms now. https://www.sciencealert.com/new-organisms-have-been-formed-using-the-first-ever-6-letter-genetic-code https://www.scienceale

There's 6-base pair organisms now. https://www.sciencealert.com/new-organisms-have-been-formed-using-the-first-ever-6-letter-genetic-code https://www.sciencealert.com/new-organisms-have-been-formed-... Also, RNA seems to work and it's possible we started out using RNA and later evolved to DNA.