<p>The HRDC (helicase and RNaseD C-terminal) domain is comprised of two orthogonally packed alpha-hairpin subdomains, and is involved in interactions with DNA and protein. </p><p>The HRDC (helicase and RNaseD C-terminal) domain is found at the C terminus of many RecQ helicases, including the human Werner and Bloom syndrome proteins [<cite idref="PUB00014060"/>]. RecQ helicases have been shown to unwind DNA in an ATP-dependent manner. The structure of the HRDC domain consists of a 4-5 helical bundle of two orthogonally packed alpha-hairpins, and as such it resembles auxiliary domains in bacterial DNA helicases and other proteins that interact with nucleic acids. A positively charged region on the surface of the HRDC domain is able to interact with DNA.</p><p>The HRDC domain is also present in eukaryotic and archaeal RNA polymerase II subunit RBP4, the N-terminal of which forms a heterodimerisation alpha-hairpin [<cite idref="PUB00032236"/>, <cite idref="PUB00007873"/>].</p>