(Science: molecular biology) The three codons, UAA known as ochre, UAG as amber and UGA as opal, that do not code for an amino acid but act as signals for the termination of protein synthesis.
They are not represented by any tRNA and termination is catalysed by protein release factors. There are two release factors in e. Coli, RF1 recognises UAA and UAG, RF2 recognises UAA and UGA. Eukaryotes have a single gTP requiring factor, eRF.
See: ochre suppressor, amber suppressor.