A dominant mutation in the gene for the Nag repressor of Escherichia coli that renders the nag regulon uninducible.

The gene nagC encodes the repressor for the nag regulon. A point mutation within the gene, which confers a super-repressor phenotype and makes the repressor insensitive to the inducer, N-acetylglucosamine 6-phosphate, has been characterized. The mutation is semi-dominant since heterozygous diploids have reduced growth rates on glucosamine and N-acetylglucosamine compared to the wild-type strain.