I'd say it's encoded in the combination of the tRNAs and the aminoacyl-tRNA synthetases, which load the appropriate amino acids on to the tRNAs. There's nothing

I'd say it's encoded in the combination of the tRNAs and the aminoacyl-tRNA synthetases, which load the appropriate amino acids on to the tRNAs. There's nothing in the tRNAs themselves which picks out a specific amino acid - that happens because the synthetases recognise specific amino acids and specific tRNAs. The synthetases are also encoded in DNA, so the fundamental point, that the code is encoded in DNA, stands.