title: DEAD-box proteins unwind duplexes by local strand separation.
abstract: DEAD-box proteins catalyze ATP-driven, local structural changes in RNA or RNA-protein complexes (RNP) during which only few RNA base pairs are separated. It is unclear how duplex unwinding by DEAD-box proteins differs from unwinding by canonical helicases, which can separate many base pairs by directional and processive translocation on the nucleic acid, starting from a helical end. Here, we show that two different DEAD-box proteins, Ded1p and Mss116p, can unwind RNA duplexes from internal as well as terminal helical regions and act on RNA segments as small as two nucleotides flanked by DNA. The data indicate that duplex unwinding by DEAD-box proteins is based on local destabilization of RNA helical regions. No directional movement of the enzymes through the duplex is involved. We propose a three-step mechanism in which DEAD-box proteins unwind duplexes as "local strand separators." This unwinding mode is well-suited for local structural changes in complex RNA or RNP assemblies.
authors.affiliation: Department of Biochemistry, Center for RNA Molecular Biology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Quansheng
authors.initials: Q
authors.lastname: Yang
authors.forename: Mark
authors.initials: M
authors.lastname: Del Campo
authors.forename: Alan M
authors.initials: AM
authors.lastname: Lambowitz
authors.forename: Eckhard
authors.initials: E
authors.lastname: Jankowsky
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008957:Models, Genetic; D009690:Nucleic Acid Conformation; D020871:RNA Stability; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000378:metabolism*; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D012330:RNA, Double-Stranded; D012331:RNA, Fungal; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D000255:Adenosine Triphosphate; C492152:DED1 protein, S cerevisiae; C058150:MSS116 protein, S cerevisiae; D053487:DEAD-box RNA Helicases