Escherichia coli NikR, a repressor with homologs in other bacteria and archaea, was identified as a potential new member of the ribbon-helix-helix (β-α-α) family of transcription factors in profile based sequence searches and in structure prediction experiments. Biophysical and biochemical characterization of the N-terminal domain of NikR show that it has many features expected of a β-α-α protein including α-helical content, dimeric solution form, concentration dependent thermal stability, and ability to bind DNA in sequence-specific manner. Mutation of a residue predicted to be important for DNA-binding reduces operator affinity but does not affect the secondary structure or stability of the protein.
