title: Structure of a hexameric RNA packaging motor in a viral polymerase complex.
abstract: Packaging of the Cystovirus varphi8 genome into the polymerase complex is catalysed by the hexameric P4 packaging motor. The motor is located at the fivefold vertices of the icosahedrally symmetric polymerase complex, and the symmetry mismatch between them may be critical for function. We have developed a novel image-processing approach for the analysis of symmetry-mismatched structures and applied it to cryo-electron microscopy images of P4 bound to the polymerase complex. This approach allowed us to solve the three-dimensional structure of the P4 in situ to 15-A resolution. The C-terminal face of P4 was observed to interact with the polymerase complex, supporting the current view on RNA translocation. We suggest that the symmetry mismatch between the two components may facilitate the ring opening required for RNA loading prior to its translocation.
authors.affiliation: Institute of Biotechnology and Faculty of Biosciences, University of Helsinki, P.O. Box 65 (Viikinkaari 1), FI-00014 University of Helsinki, Finland.
authors.forename: Juha T
authors.initials: JT
authors.lastname: Huiskonen
authors.forename: Harri T
authors.initials: HT
authors.lastname: Jäälinoja
authors.forename: John A G
authors.initials: JA
authors.lastname: Briggs
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Fuller
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Butcher
mesh_terms: D020285:Cryoelectron Microscopy / Q000379:methods; D018360:Crystallography, X-Ray / Q000379:methods; D017910:Cystoviridae / Q000201:enzymology* / Q000502:physiology; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000648:ultrastructure*; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure*; D012367:RNA, Viral / Q000378:metabolism; D017361:Viral Nonstructural Proteins / Q000737:chemistry / Q000648:ultrastructure*; D019065:Virus Assembly
chemical_list: D046912:Multiprotein Complexes; D012367:RNA, Viral; D017361:Viral Nonstructural Proteins; D012321:DNA-Directed RNA Polymerases