title: Repetitive RNA unwinding by RNA helicase A facilitates RNA annealing.
abstract: Helicases contribute to diverse biological processes including replication, transcription and translation. Recent reports suggest that unwinding of some helicases display repetitive activity, yet the functional role of the repetitiveness requires further investigation. Using single-molecule fluorescence assays, we elucidated a unique unwinding mechanism of RNA helicase A (RHA) that entails discrete substeps consisting of binding, activation, unwinding, stalling and reactivation stages. This multi-step process is repeated many times by a single RHA molecule without dissociation, resulting in repetitive unwinding/rewinding cycles. Our kinetic and mutational analysis indicates that the two double stand RNA binding domains at the N-terminus of RHA are responsible for such repetitive unwinding behavior in addition to providing an increased binding affinity to RNA. Further, the repetitive unwinding induces an efficient annealing of a complementary RNA by making the unwound strand more accessible. The complex and unusual mechanism displayed by RHA may help in explaining how the repetitive unwinding of helicases contributes to their biological functions.
authors.affiliation: Department of Physics, University of Illinois, Urbana, IL 61801, USA Institute for Genomic Biology, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Hye Ran
authors.initials: HR
authors.lastname: Koh
authors.affiliation: Lady Davis Institute for Medical Research and McGill AIDS Centre, Jewish General Hospital, Montreal, Quebec, H3T 1E2, Canada Department of Medicine, McGill University, Montreal, Quebec, H3G 1Y6, Canada.
authors.forename: Li
authors.initials: L
authors.lastname: Xing
authors.affiliation: Lady Davis Institute for Medical Research and McGill AIDS Centre, Jewish General Hospital, Montreal, Quebec, H3T 1E2, Canada Department of Medicine, McGill University, Montreal, Quebec, H3G 1Y6, Canada.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Kleiman
authors.affiliation: Institute for Genomic Biology, University of Illinois, Urbana, IL 61801, USA Department of Bioengineering, University of Illinois, Urbana, IL 61801, USA Physics Frontier Center (Center of Physics for Living Cells), University of Illinois, Urbana, IL 61801, USA Biophysics and Computational Biology, 1110 W. Green St., Urbana, IL 61801, USA smyong@illinois.edu.
authors.forename: Sua
authors.initials: S
authors.lastname: Myong
mesh_terms: D053487:DEAD-box RNA Helicases / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D017434:Protein Structure, Tertiary; D012330:RNA, Double-Stranded / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry
chemical_list: D012330:RNA, Double-Stranded; D016601:RNA-Binding Proteins; D053487:DEAD-box RNA Helicases