Regulation of Escherichia coli purF. Mutations that define the promoter, operator, and purine repressor gene.

Mutations were constructed in vitro which identify the -35 promoter element and the operator site of the Escherichia coli purF operon as well as confirm the -10 promoter sequence. The operator was localized by a two-base change at positions -26 and -27, relative to the start of transcription. This mutation abolished repression of a purF-lacZ fusion. In the wild-type, repression of single copy and multicopy purF-lacZ constructs was equally effective. This indicates that cells contain a greater than 100-fold excess of purR-encoded repressor than is needed to regulate the chromosomal purF operon. Thus, cells contain sufficient repressor to regulate the other pur regulon genes. Two independent purR mutations were isolated which abolished repression of purF and purF-lacZ. We conclude that there is a single repressor protein-operator regulatory system to sense purine or purine nucleotide pools.