Speculation about it was fruitful during the 1950s, but the code was cracked by experiment. Subsequently, within five years, the entire genetic code was deciphered. RNA, the close kin and working partner to DNA, provided the key to the code. While DNA resides almost entirely in the cell nucleus, protein synthesis takes place in the cytoplasm, where RNA is found. On molecular workbenches known as ribosomes, sequences of RNA, transcribed from stretches of DNA, serve as instructions for manufacturing proteins.
Protein synthesis represents the fundamental work of the genes.
Nirenberg's series of key experiments, carried out initially with German scientist Johann Matthaei, employed test-tube techniques. They also added amino acids, one of which was radioactively tagged. These molecules were made entirely of the amino acid phenylalanine. With four bases, there were 64 possible triplets. Both AAG and AAA, for example, code for the amino acid lysine.