The RecQ helicase from Deinococcus radiodurans (DrRecQ) is unusual from other DNA helicases in that it utilizes its three ‘Helicase and RNaseD C-terminal (HRDC1,2 and 3) domains to regulate its activity.Except its most C-terminal HRDC3 motif,the structures of other HRDC domains were never reported.In this study,we determined the solution structure of the separated and the most N-terminal DrRecQ HRDC1 domain,revealing a globular fold that resembles known DNA binding domains.We thus characterized its DNA-binding activities by fluorescence anisotropy assay,indicating that HRDC 1 does not preferentially bind to any DNA substrate,and it is just an auxiliary DNA binding domain of RecQ_Ct domain with weak binding affinities (KD > ~10 μM).