I hate to break it to you, but they didn’t spell using the four letter alphabet, what they did was utilize DNA to produce amino acids in a certain sequence. That’s not spelling with DNA, that’s spelling with the letters that have been artificially assigned to each amino acid.
Spelling nonetheless. Just using a different language. :-).
Where do you get this idea that the DNA code is more than the 4 bases. Watson, Crick and Rosalind Franklin were wrong and GGG is right?