Numerous bacterial transcription regulatory proteins bind DNA via a helix-turn-helix (HTH) motif. These proteins are very diverse, but for convenience may be grouped into subfamilies on the basis of sequence similarity. One such family groups together a range of proteins, including ascG, ccpA, cytR, ebgR, fruR, galR, galS, lacI, malI, opnR, purF, rafR, rbtR and scrR [<cite idref="PUB00002732"/>, <cite idref="PUB00005082"/>]. Within this family, the HTH motif is situated towards the N terminus.<p>This entry represents the bacterial helix-turn-helix transcriptional repressor PurR family. The purR gene encodes a transcriptional repressor of the HTH-type which is responsible for controlling the syntehsis of enzymed involved in purine biosynthesis [<cite idref="PUB00054593"/>]. PurR is dimeric and consists of an N-terminal domain for DNA binding and a C-terminal domain which is responsible for corepressor (hypoxanthine and guanine) binding. Dimerisation sites are present in the C-terminal domain and binding of corepressors is cooperative [<cite idref="PUB00054594"/>].</p> Transcription regulator HTH, PurR