Protein Displacement by DExH/D "RNA Helicases" Without Duplex Unwinding

Abstract

Members of the DExH/D superfamily of nucleic acid–activated nucleotide triphosphatases are essential for virtually all aspects of RNA metabolism, including pre–messenger RNA splicing, RNA interference, translation, and nucleocytoplasmic trafficking. Physiological substrates for these enzymes are thought to be regions of double-stranded RNA, because several DExH/D proteins catalyze strand separation in vitro. These “RNA helicases” can also disrupt RNA-protein interactions, but it is unclear whether this activity is coupled to duplex unwinding. Here we demonstrate that two unrelated DExH/D proteins catalyze protein displacement independently of duplex unwinding. Therefore, the essential functions of DExH/D proteins are not confined to RNA duplexes but can be exerted on a wide range of ribonucleoprotein substrates.