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. Author manuscript; available in PMC: 2018 May 22.
Published in final edited form as: Nat Rev Microbiol. 2017 Mar 27;15(6):338–350. doi: 10.1038/nrmicro.2017.15

Figure 2. Mechanisms of stepwise regulation of the Zur regulon.

Figure 2

Under conditions of Zn(II) sufficiency (right), the dimeric Zur repressor is present in its fully metallated (Zur2:Zn4) state and the full Zur regulon is repressed. As Zn(II) levels fall, the first sets of genes (see Fig. 3) are derepressed as Zur transitions to the intermediate metallated form (Zur2:Zn3; middle) that binds DNA with lower affinity. As Zn(II) levels fall further, the remaining, more tightly bound, Zn(II) ion dissociates leading to formation of Zur with only the structural Zn(II) site is occupied ( Zur2:Zn2; left). This leads to derepression of additional adaptive responses, including the expression of the alternate folate synthesis enzyme FolEB and an alternate S14 ribosomal protein.