Brenner examined certain mutations in a single gene that influence the head protein and found that the head protein of every mutant is a small peptide chain than that of the wild type. He analyzed the ends of the shorten proteins and related with the wild type protein and recorded the next amino acid that would have been introduced to continue the wild type chain.
The amino acids that are needed to be introduced to prolong the wild-type chain and their codons are as follows:
• Glutamine – CAA, CAG
• Lysine – AAA, AAG
• Glutamic acid – GAA, GAG
• Tyrosine – UAU, UAC
• Tryptophan – UGG
• Serine – UCU, UCC, UCA, UCG, AGU, AGC.
Particularly, each of the codons like CAG, AAG, GAG, UAU, UAC, UGG, and UCG can mutate to the codon UAG, which is an amber codon or first stop codon by a single change in the deoxyribonucleic acid nucleotide pair.