Crick, Brenner et al. experiment

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The Crick, Brenner et al. experiment was a scientific experiment performed in 1961 by Francis Crick and Sydney Brenner. They demonstrated that three bases of DNA code for one amino acid in the genetic code. The experiment elucidated the nature of gene expression and frameshift mutations.

In the experiment, proflavin-induced mutations of the T4 bacteriophage gene, rIIB, were isolated. Proflavin causes mutations by inserting itself between DNA bases, typically resulting in insertion or deletion of a single base pair.

The mutants produced by Crick and Brenner could not produce functional rIIB protein because the insertion or deletion of a single nucleotide caused a frameshift mutation. Mutants with two or four nucleotides inserted or deleted were also nonfunctional. However, the mutant strains could be made functional again by using proflavin to insert or delete a total of three nucleotides. This proved that the genetic code uses a codon of three DNA bases that corresponds to an amino acid.


  1. Crick FH, Barnett L, Brenner S, Watts-Tobin RJ. General nature of the genetic code for proteins. Nature. 1961 Dec 30;192:1227-32. PubMed: Entrez PubMed 13882203.

See also

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