title: Structure of the Rho transcription terminator: mechanism of mRNA recognition and helicase loading.
abstract: In bacteria, one of the major transcriptional termination mechanisms requires a RNA/DNA helicase known as the Rho factor. We have determined two structures of Rho complexed with nucleic acid recognition site mimics in both free and nucleotide bound states to 3.0 A resolution. Both structures show that Rho forms a hexameric ring in which two RNA binding sites--a primary one responsible for target mRNA recognition and a secondary one required for mRNA translocation and unwinding--point toward the center of the ring. Rather than forming a closed ring, the Rho hexamer is split open, resembling a "lock washer" in its global architecture. The distance between subunits at the opening is sufficiently wide (12 A) to accommodate single-stranded RNA. This open configuration most likely resembles a state poised to load onto mRNA and suggests how related ring-shaped enzymes may be breached to bind nucleic acids.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, 239 Hildebrand Hall, #3206, Berkeley, CA 94720, USA.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Skordalakes
authors.forename: James M
authors.initials: JM
authors.lastname: Berger
mesh_terms: D001665:Binding Sites / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D008958:Models, Molecular; D008968:Molecular Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics; D020365:RNA Helicases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012234:Rho Factor / Q000235:genetics* / Q000378:metabolism*; D013728:Terminator Regions, Genetic / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D012234:Rho Factor; D020365:RNA Helicases