Sandbox Reserved 1053: Difference between revisions

Czr A is a transcriptional repressor protein responsible for the regulation of the Czr operon. The Czr operon contains genes for the proteins Czr A and Czr B. Czr B is a Zinc transport protein which moves Zn²⁺ out of a cell while Czr A regulates this process by controlling expression level of Czr B. When relatively low amounts of zinc are present in the cell Czr A will bind to DNA, preventing the progression of RNA polymerase and thus inhibiting expression of Czr B. Decreased expression of Czr B results in the ability of the cell to retain Zn²⁺ more readily. Because Czr A and Czr B are transcribed as part of the same operon, an inhibitor of Czr A must be readily available to allow full transcription of Czr B when necessary. Czr A is noncompetitively inhibited by the binding of two Zn²⁺ ions, which is ideal in that this allows for expression of Czr B, a Zn²⁺ transporter to be dependent on the relative amount of Zn²⁺ in the cell.  Czr A displays two different conformations; the first typically binds DNA and has relatively low affinity for Zn²⁺, in this conformation the <scene name='69/694220/A5_helices__dna_binding/1'>a5 helices are open</scene>. The <scene name='69/694220/A5_helices_dna_binding/1'>a5 helices swing down</scene> to achieve the other conformation which binds two Zn²⁺ ions and has relatively low affinity for DNA.