In 1954 George Gamow published a paper with regard to the ‘Possible Relation between Deoxyribonucleic Acid and Protein Structures’. Crick dismissed his ‘key-and-lock’ idea because their model provided no such possibility. We now have model that would potentially serve such a purpose.
“ Gamow’s “code” was unusual in several ways. Each amino acid was coded by a triplet of bases (actually several triplets, related by symmetry), but the triplets standing for successive amino acids overlapped. For example, if a small part of the sequence was ... GGAC ... , Then GGA stood for one amino acid, and GAC for the next one.....
Jim and I had several objections to Gamow’s ideas. We rather doubted whether the cavities in DNA were capable of doing the job. We worried about his symmetry assumptions, and we didn’t like the idea of DNA coding directly for proteins. RNA seemed a more likely candidate, but perhaps RNA could fold up into a structure that could form the necessary cavities.”
Francis Crick - What Mad Pursuit (p93)