Isolation of the Self-Regulated Repressor Protein of the Hut Operons of Salmonella typhimurium

In Salmonella typhimurium the structural genes of the enzymes responsible for histidine utilization (hut) are clustered in two adjacent operons. A single repressor regulates both operons. The repressor itself is a member of one of the hut operons and, thus, regulates its own synthesis. We have assayed the hut repressor by its ability to bind radioactive DNA to nitrocellulose filters. The binding is specific for DNA bearing the hut operons, and the binding is abolished by the inducer, urocanate. As a member of one of the hut operons, the repressor is inducible, subject to catabolite repression, and affected by a promoter mutation.