Studies on deo operon regulation in Escherichia coli: cloning and expression of the deoR structural gene

Recombinant plasmid pBR322 derivatives containing the Escherichia coli deoR structural gene (coding for one repressor of the deo operon) and a mutant allele of the cmlA gene (chromosomally encoded chloramphenicol resistance) have been constructed and the positions of these genes on a 6.3-kb EcoRI fragment have been determined. Transformation of an E. coli deoR single mutant with any of the deoR+ plasmids resulted in complementation of the chromosomal deoR mutation. More importantly, however, transformation of a deoR cytR double mutant with the deoR+ plasmids also resulted in complete repression of Deo enzyme synthesis. Based on these data, we conclude that transcription of the deo operon initiating from both the cAMP/CRP-independent promoter-operator site, PO1, and the cAMP/CRP-dependent promoter-operator site, PO2, is negatively controlled by the deoR-encoded repressor, whereas the cytR-encoded repressor regulates deo operon expression only from the cAMP/CRP-dependent promoter-operator site, PO2.