XRE (Xenobiotic Response Element) family of transcription factors comprises the second most frequently occurring regulator family in Bacteria that control various and diverse metabolic functions. XRE-family proteins were found both in Bacteria, Archaea, and bacteriophages . Among well-studied members of the XRE family are the lambda and Cro repressors of lambda bacteriophage, prophage repressor Xre, development regulator, restriction-modification system control proteins, antitoxin proteins, bacterial methylases etc [15634675, 18502921, 21722202]. Environmental stimuli that activate XRE-family proteins vary from protein-protein interaction to direct binding of small molecule effectors.
XRE-family regulators share a characteristic N-terminal HTH DNA binding domain (PF01381), while C-terminal regulatory region is highly variable [18502921