In this paper Crick, Brenner, and their collaborators described a very elegant series of genetic experiments by which they
proved that the genetic code for protein was a triplet code. They used an acridine dye, proflavin, to induce mutations in
a specific, well-studied gene of a virus, a so-called bacteriophage, that attacked the bacterium Escherichia coli. The effect
of proflavin was to either eliminate a single nucleotide from the gene or to add a nucleotide, each of which had the effect
of rendering the virus incapable of synthesizing a particular protein. After a sequence of three such additions or deletions,
the nucleotide sequence of the gene once again come into frame, and synthesis of the protein resumed. This proved that the
nucleotide sequence which carried the genetic information was to be read three (or, less likely, six) nucleotides at a time
proceeding from a fixed starting point.
Simultaneous with but independent of Crick and Brenner's genetic experiments, Marshall Nirenberg, a biochemist at the
National Institutes of Health, developed direct biochemical evidence of the triple code. Together, they laid the foundation
for the deciphering of the genetic code over the course of the next half-decade.
Crick and Brenner's experiment with acridine mutants was another fruitful application of genetic studies of the rII region
of bacteriophage T4, an experimental system developed by Seymour Benzer in the early 1950s that allowed fine-structure mapping
of a gene at the nucleotide level, two decades before techniques for direct sequencing of DNA were first developed.
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1961-12-30 (December 30, 1961)
Watts-Tobin, R. J.
Periodical: Crick, Francis, Leslie Barnett, Sydney Brenner, and R. J. Watts-Tobin. "General Nature of the Genetic Code for Proteins."
Nature 192, 4809 (30 December 1961): 1227-1232. Article. 6 Images.
Nature Publishing Group
Reproduced with permission of the Nature Publishing Group.