Almost immediately, Marshall Nirenberg and J. Heinrich Matthaei put it to use to form the first three-nucleotide RNA codons, which coded for the amino acid phenylalanine.
Instead, it was discovered by Mario Capecchi in 1967 that tRNAs do not ordinarily recognize stop codons at all, and that what he named "release factor" was not a tRNA molecule, but a protein.
Scans for natural selection showed that most codons of the SLE virus ORF were evolving neutrally or under negative selection.
Steffen Mueller at the Stony Brook University designed a live virus vaccine for polio in which the pathogen was engineered to have synonymous codons replace naturally-occurring ones in the genome.