Two operator sites separated by 599 base pairs are required for deoR repression of the deo operon of Escherichia coli.

DeoP1 and deoP2 promoter fragments from the deo operon of Escherichia coli have been transcriptionally fused to the galactokinase gene. From single-copy expression of these fusions it is shown that the deoR binding site of both deoP1 and deoP2 are necessary to achieve full repression of the deo operon by the deoR repressor. Repression of the promoters can be achieved either by supplying extra deoR repressor in trans or by introduction of an extra deoR binding site at a position between 224 and 997 bp upstream of the promoter. Furthermore, the deoP2 promoter is shown to be regulated in a cumulative way by both the deoR and the cytR repressors, while deoP1 is only regulated by the deoR repressor. DeoP2 is a strong promoter being 20 times stronger than araPBAD and four times stronger than deoP1.