<p>The Crp-type HTH domain is a DNA-binding, winged helix-turn-helix (wHTH)domain of about 70-75 amino acids present in transcription regulators of thecrp-fnr family, involved in the control of virulence factors, enzymes ofaromatic ring degradation, nitrogen fixation, photosynthesis, and varioustypes of respiration. The Crp-Fnr family is named after the first membersidentified in <taxon tax_id="562">Escherichia coli</taxon>: the well characterised cyclic AMP receptor protein CRPor CAP (catabolite activator protein) and the fumarate and nitrate reductaseregulator Fnr. Crp-type HTH domain proteins occur in most bacteria and inchloroplasts of red algae. The DNA-binding HTH domain is located in theC-terminal part; the N-terminal part of the proteins of the Crp-Fnr familycontains a nucleotide-binding domain and adimerization/linker helix occurs in between. The Crp-Fnr regulatorspredominantly act as transcription activators, but can also be importantrepressors, and respond to diverse intracellular and exogenous signals, suchas cAMP, anoxia, redox state, oxidative and nitrosative stress, carbonmonoxide, nitric oxide or temperature [<cite idref="PUB00004442"/>, <cite idref="PUB00013967"/>].</p> Helix-turn-helix motif, Crp-type