DNA-binding and enzymatic domains of the bifunctional biotin operon repressor (BirA) of Escherichia coli.

The negative regulation of the biotin biosynthetic (bio) operon in Escherichia coli is mediated by the bifunctional birA gene product, which serves as the bio repressor and biotin-activating enzyme. Nucleotide sequence analysis of 18 mutations in the birA gene was employed to study the DNA-binding and enzymatic functions of the BirA protein. The results indicate that a predicted helix-turn-helix structure, from amino acid (aa) positions 18 to 39 within the 321-aa BirA protein, may be responsible for sequence-specific DNA binding, whereas the temperature-sensitive mutations affecting biotin activation are found in two regions from aa positions 83-119 and 189-235.