Frameshift Mutations in the Lactose Operon of E. coli

Polar mutants, first described in the lactose operon of Escherichia coli by Jacob and Monod (1961a, b) and Franklin and Luria (1961), have played an essential role in the development of the concept of the operon as a unit of coordinate genetic expression. This class of mutation, occurring within a structural gene (in contrast to mutations in operator or regulator genes) and having the unusual property of affecting the expression of genes other than the mutated gene, was a clear violation of the “one gene-one enzyme” postulate of Beadle and Tatum (1941). Polar mutations in the structural gene for β-galactosidase lead to a decreased synthesis of β-galactoside permease and thiogalactoside transacetylase.