REGULATED EXPRESSION OF A REPRESSOR PROTEIN - FADR ACTIVATES ICLR

The control of the glyoxylate bypass operon (aceBAK) of Escherichia co li is mediated by two regulatory proteins, IclR and FadR. IclR is a re pressor protein which has previously been shown to bind to a site whic h overlaps the aceBAK promoter. FadR is a repressor/activator protein which participates in control of the genes of fatty acid metabolism. A sequence just upstream of the iclR promoter hears a striking resembla nce to FadR binding sites found in the fatty acid metabolic genes. The in vitro binding specificity of FadR, determined by oligonucleotide s election, was in good agreement with the sequences of these sites. The ability of FadR to bind to the site associated with iclR was demonstr ated by gel shift and DNase I footprint analyses. Disruption of fadR o r inactivation of the FadR binding site of iclR decreased the expressi on of an iclR::lacZ operon fusion, indicating that FadR activates the expression of iclR. It has been reported that disruption of fadR incre ases the expression of aceBAK. We observed a similar increase when we inactivated the FadR binding site of an iclR(+) allele. This result su ggests that FadR regulates aceBAK indirectly by altering the expressio n of IclR.