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.