Transcription regulator HTH, Crp 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. This family groups together a range of proteins, including anr, crp, clp, cysR, fixK, flp, fnr, fnrN, hlyX and ntcA [<cite idref="PUB00013967"/>, <cite idref="PUB00013968"/>]. Within this family, the HTH motif is situated towards the C terminus.