Cracking the code

Scientists reveal how the sequence of DNA’s four chemical subunits encode the instructions for the creation of the amino acids that make up proteins. One team including Francis Crick and Sydney Brenner discovers that it’s a triplet code, with each sequence of three subunits, or “genetic letters,” coding for one amino acid. In the same year, Marshall Nirenberg and Heinrich Matthaei report the three-letter sequence associated with one particular amino acid, jump-starting efforts to identify more.