Copper-sensitive repressor that has a key role in copper homeostasis. Negatively regulates expression of the copZA operon and of ycnJ. In the absence of copper ions, binds with high affinity to the copZA promoter and represses the transcription. In the presence of copper ions, CsoR binds Cu(1+), which significantly decreases its DNA binding affinity and leads to the transcription of the genes. Homotetramer. Binds DNA with a stoichiometry of 2 tetramers per DNA. Cells lacking this gene display a slightly enhanced ability to grow into medium containing high levels of copper. Can also bind other divalent metal ions (zinc, cobalt and nickel), but these metals are poor regulators of DNA binding. Belongs to the CsoR family.