Characterization and transcriptional regulation of the modABCD genes for molybdenum transport in Escherichia coli.

The mod genes coding for molybdenum transport system were isolated from Escherichia coli by means of complementation of the tor mutation that causes no synthesis of some molybdenum-containing enzymes. The nucleotide sequence of 3048-base pair showed four open reading frames including the previously reported modC gene. The genes were named modA, modB, modC, and modD. Promoter analysis by lacZ assay and primer extension showed the genes modA and modB individually have their own promoters. No transcriptional regulation of the two genes were observed in the presence of molybdate, nitrate, and oxygen in E. coli strain DH5 alpha.