title: RNA packaging device of double-stranded RNA bacteriophages, possibly as simple as hexamer of P4 protein.
abstract: Genomes of complex viruses have been demonstrated, in many cases, to be packaged into preformed empty capsids (procapsids). This reaction is performed by molecular motors translocating nucleic acid against the concentration gradient at the expense of NTP hydrolysis. At present, the molecular mechanisms of packaging remain elusive due to the complex nature of packaging motors. In the case of the double-stranded RNA bacteriophage phi 6 from the Cystoviridae family, packaging of single-stranded genomic precursors requires a hexameric NTPase, P4. In the present study, the purified P4 proteins from two other cystoviruses, phi 8 and phi 13, were characterized and compared with phi 6 P4. All three proteins are hexameric, single-stranded RNA-stimulated NTPases with alpha/beta folds. Using a direct motor assay, we found that phi 8 and phi 13 P4 hexamers translocate 5' to 3' along ssRNA, whereas the analogous activity of phi 6 P4 requires association with the procapsid. This difference is explained by the intrinsically high affinity of phi 8 and phi 13 P4s for nucleic acids. The unidirectional translocation results in RNA helicase activity. Thus, P4 proteins of Cystoviridae exhibit extensive similarity to hexameric helicases and are simple models for studying viral packaging motor mechanisms.
authors.affiliation: Department of Biosciences and Institute of Biotechnology, FIN-00014, University of Helsinki, Finland.
authors.forename: Denis E
authors.initials: DE
authors.lastname: Kainov
authors.forename: Markus
authors.initials: M
authors.lastname: Pirttimaa
authors.forename: Roman
authors.initials: R
authors.lastname: Tuma
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Butcher
authors.forename: George J
authors.initials: GJ
authors.lastname: Thomas
authors.forename: Dennis H
authors.initials: DH
authors.lastname: Bamford
authors.forename: Eugene V
authors.initials: EV
authors.lastname: Makeyev
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000595:Amino Acid Sequence; D017126:Bacteriophage phi 6 / Q000378:metabolism; D002213:Capsid; D020285:Cryoelectron Microscopy; D017910:Cystoviridae / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D006868:Hydrolysis; D007700:Kinetics; D008027:Light; D008969:Molecular Sequence Data; D009502:Neutrons; D012313:RNA / Q000737:chemistry* / Q000378:metabolism; D020365:RNA Helicases / Q000737:chemistry; D012330:RNA, Double-Stranded / Q000737:chemistry* / Q000378:metabolism; D012367:RNA, Viral / Q000737:chemistry; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman; D013997:Time Factors; D014544:Uridine Triphosphate / Q000494:pharmacology; D019065:Virus Assembly
chemical_list: D012330:RNA, Double-Stranded; D012367:RNA, Viral; D012313:RNA; D000255:Adenosine Triphosphate; D020365:RNA Helicases; D014544:Uridine Triphosphate