<p>Many bacterial transcription regulation proteins bind DNA through a'helix-turn-helix' (HTH) motif. One major subfamily of these proteins [<cite idref="PUB00004444"/>, <cite idref="PUB00003566"/>] is related to the arabinose operon regulatory protein AraC [<cite idref="PUB00004444"/>, <cite idref="PUB00003566"/>. Except for celD [<cite idref="PUB00001933"/>], all of these proteins seem to be positive transcriptional factors.</p><p>Although the sequences belonging to this family differ somewhat in length, in nearly every case the HTH motif is situated towards the C terminus in the third quarter of most of the sequences. The minimal DNA binding domain spans roughly 100 residues and comprises two HTH subdomains; the classical HTH domain and another HTH subdomain with similarity to the classical HTH domain but with an insertion of one residue in the turn-region. The N-terminal and central regions of these proteins are presumed to interact with effector molecules and may be involved in dimerisation [<cite idref="PUB00004817"/>].</p><p>The known structure of MarA (<db_xref db="SWISSPROT" dbkey="P27246"/>) shows that the AraC domain is alpha helical and shows the two HTH subdomains both bind the major groove of the DNA. The two HTH subdomains are separated by only 27angstroms, which causes the cognate DNA to bend.</p><p>This entry representsthe full AraC domain containing the two HTH subdomains.</p> Helix-turn-helix, AraC type, DNA binding