The ModE Gene Product Mediates Molybdenum-dependent Expression of Genes for the High-affinity Molybdate Transporter and ModG in Azotobacter Vinelandii

The Azotobacter vinelandii mod locus, which is involved in high-affinity molybdate transport and the early event in Mo metabolism, consists of two divergently transcribed operons, modG and modEABC. modA, modB and modC encode the components of the high-affinity molybdate transporter, and modG encodes a Mo-binding protein. High concentrations of Mo repressed transcription of both operons. The modEABC operon was also repressed by tungstate and to a lesser extent by vanadate. modE, the first gene in the modEABC operon, controlled the Mo-dependent transcription of both operons. It was not involved in the metal regulation of alternative nitrogenase gene expression. Although a modE mutant constitutively expressed genes encoding the molybdate transporter, it had a reduced rate of Mo accumulation.