<P> Stop codons were historically given many different names, as they each corresponded to a distinct class of mutants that all behaved in a similar manner . These mutants were first isolated within bacteriophages (T4 and lambda), viruses that infect the bacteria Escherichia coli . Mutations in viral genes weakened their infectious ability, sometimes creating viruses that were able to infect and grow within only certain varieties of E. coli . </P> <Dl> <Dt> amber mutations (UAG) </Dt> <Dd> were the first set of nonsense mutations to be discovered, isolated by Richard Epstein and Charles Steinberg and named after their friend Harris Bernstein (whose last name means "amber" in German). </Dd> </Dl> <Dt> amber mutations (UAG) </Dt> <Dd> were the first set of nonsense mutations to be discovered, isolated by Richard Epstein and Charles Steinberg and named after their friend Harris Bernstein (whose last name means "amber" in German). </Dd>

What codons signal the start and stop of protein synthesis