This domain is found in archaea, and is about 40 amino acids in length. It has a single completely conserved residue E that may be functionally important. It is found in the archaeal DNA dependent RNA polymerase. The domain is a 'helix-turn-helix' (HTH) domain in the Rpo13 subunit of the RNA polymerase. This domain is involved in downstream DNA binding, and the entire subunit has also been implicated in contacting transcription factor II B.