MadSci Network: Molecular Biology

Re: What is the story behind the naming convention of stop codons?

Date: Wed Mar 29 15:09:15 2000
Posted By: Michael Onken, Admin, MadSci Network
Area of science: Molecular Biology
ID: 954351397.Mb

The story I had been told (back in '86) was that the names corresponded to the colors of the plaques formed by mutant bacteriophages. This, too, seemed anecdotal, so I did some searching through the stacks and found several related articles, the three most relevent of which are cited below. Here's what I found from my short investigation. In 1961 Seymour Benzer and Sewell Champe described a new subset of the rII class of T4 bacteriophage mutants which made the phage host-selective, that is these particular mutants could infect one of two strains of E. coli but not both. They classified these mutants as "Ambivalent" (Amb) rII mutants. Two years later, R.H. Epstein, working in Geneva, and R.S. Edgar, working at CalTech, collaborated to characterize several other T4 bacteriophage mutants that were either temperature sensitive (Epstein) or host-selective (Edgar). They dubbed the host-selective mutations "Amber". It is suggestive that "Amber" may be a variation on "ambivalent rII", the original name for these mutants, though the assay they used to test for infection involved spectroscopic analyses of lysed liquid cultures, which, I can attest, are amber in color. In 1965, Sydney Brenner described the link between amber mutants and stop codons, and described "ochre" mutants as an analogous but separate set of mutants relating to a different codon: ochre being a color similar to but not the same as amber. When I was first introduced to genetic engineering in 1982, those were the only two names I heard, and I often wondered why UGA didn't have a color name as well. Apparently UGA usage is not variable between E. coli strains, such that this mutation does not produce host-selectivity in T4 phage, and thus wasn't associated with a "color" mutant.

Benzer S., and Champe S.P. (1961), "Ambivalent rII Mutants of Phage T4," Proc. Natl. Acad. of Sci. USA 47: 1025
Epstein R.H., et al. (1963), Physiological Studies of Conditional Lethal Mutants of Bacteriophage T4D," Cold Spr. Harb. Symp. on Quant. Biol. 28: 375
Brenner S., et al. (1965), "Genetic Code: the 'Nonsense' Triplets for Chain Termination and their Supression," Nature 206: 994

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