Transcriptional regulation of the moe (molybdate metabolism) operon of Escherichia coli

Regulation of transcription of the Escherichia coli moe operon, which codes for proteins connecting molybdate metabolism, molybdopterin synthesis, and apomolybdoenzyme synthesis, was investigated. Expression of the moe operon was independent of genes coding for molybdate transport and Mo-cofactor bi osynthesis. Expression of moeA-lacZ increased during anaerobic growth (2.5- fold over the aerobic value) and in the presence of nitrate and trimethylam ine N-oxide (3.5- and 1.5-fold, respectively). The nitrate-dependent increa se in moe expression required the NarL protein, while the anaerobiosis-depe ndent increase in moeA-lacZ expression required Are proteins. ArcA-phosphat e and not ArcA bound to the DNA upstream of mot, shifted the electrophoreti c mobility of moe promoter DNA, and protected the DNA from DNase I hydrolys is. Nitrate-independent transcription of moeA-lacZ was repressed by the FNR protein, which also protected mop operator DNA from DNase I hydrolysis. Th ese results show that ArcA-phosphate and FNR have opposite effects on the t ranscriptional regulation of the moe operon, and the combined action of the two redox regulators modulate the level of Mo-cofactor in the cell. Appare ntly, the control of synthesis of Mo-cofactor and the apomolybdoenzymes nit rate reductase and trimethylamine N-oxide reductase are coupled at the leve l of the mop operon.