Genetic regulation of the glyoxylate shunt in Escherichia coli K-12.

The expression of the glyoxylate shunt enzymes is required for growth of Escherichia coli on acetate or fatty acids as a sole carbon source. The genes for the two unique enzymes of the glyoxylate shunt, aceA and aceB, are located at 90 min on the E. coli K-12 genetic map. Polar mutations in the aceB gene eliminate aceA gene function, suggesting that these genes constitute an operon and the direction of transcription is from aceB to aceA. Mu d (Ap lac) fusions with the aceA gene have been constructed to study the regulation of the ace operon. Expression of the ace operon is under the transcriptional control of two genes: the iclR gene, which maps near the ace operon, and the fadR gene, which maps at 25 min, and is also involved in the regulation of the fatty acid degradation (fad) regulon. Merodiploid studies demonstrated that both the iclR and fadR genes regulate the glyoxylate shunt in a trans-dominant manner.