OMG. Clever! And I was at some point going "hmm... 4 letters are like nucleotides". Nahhhh that's not it. Cool, I think I know, just now need the right tool...
EDIT: I participate in this challenge (sent by steemit.chat)
Interestingly enough, my strategy of splitting into triplets initially would have worked with one more tweak , but without the hint I likely would have been stuck trying to figure out how to make the missing letters of the code we are supposed to re-encode with this method.