Structural domains comprising this superfamily share the structure of the helicase and RNaseD C-terminal (HRDC) domain, involved in interactions with both DNA and protein, is conserved among members of the RecQ helicase family, including the human Werner and Bloom syndrome proteins, and regulates helicase activity by virtue of variations in its surface residues PMID:10647186. RecQ helicases 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, structure which 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.

The HRDC domain is also found in eukaryotic and archaeal RNA polymerase II subunit RBP4 PMID:15591044,PMID:11741548.