dsRBM1 and a proline-rich domain of RNA helicase A can form a composite binder to recognize a specific dsDNA.

The double-stranded RNA-binding motif (dsRBM) is a widely distributed motif frequently found within proteins with sequence non-specific RNA duplex-binding activity. In addition to the binding of double-stranded RNA, some dsRBMs also participate in complex formation via protein-protein interactions. Interestingly, a lot of proteins containing multiple dsRBMs have only some of their dsRBMs with the expected RNA duplex-binding competency proven, while the functions of the other dsRBMs remain unknown. We show here that the dsRBM1 of RNA helicase A (RHA) can cooperate with a C-terminal domain of proline-rich content to gain novel nucleic acid-binding activities. This integrated nucleic acid-binding module is capable of associating with the consensus sequences of the constitutive transport element (CTE) RNA of type D retrovirus against RNA duplex competitors. Remarkably, binding activity for double-stranded DNA corresponding to the consensus sequences of the cyclic-AMP responsive element also resides within this composite nucleic acid binder. It thus suggests that the dsRBM fold can be used as a platform for the building of a ligand binding module capable of non-RNA macromolecule binding with an accessory sequence, and functional assessment for a newly identified protein containing dsRBM fold should be more cautious.