Nitrogen metabolism genes of Bacillus subtilis are regulated by the availability of rapidly metabolizable nitrogen sources, but not by any mechanism analogous to the two‐component Ntr regulatory system found in enteric bacteria. Instead, at least three regulatory proteins independently control the expression of gene products involved in nitrogen metabolism in response to nutrient availability. Genes expressed at high levels during nitrogen‐limited growth are controlled by two related proteins, GlnR and TnrA, which bind to similar DNA sequences under different nutritional conditions. The TnrA protein is active only during nitrogen limitation, whereas GlnR‐dependent repression occurs in cells growing with excess nitrogen. Although the nitrogen signal regulating the activity of the GlnR and TnrA proteins is not known, the wild‐type glutamine synthetase protein is required for the transduction of this signal to the GlnR and TnrA proteins. Examination of GlnR‐ and TnrA‐regulated gene expression suggests that these proteins allow the cell to adapt to growth during nitrogen‐limited conditions. A third regulatory protein, CodY, controls the expression of several genes involved in nitrogen
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