RNA Packaging Device of Double-stranded RNA Bacteriophages, Possibly as Simple as Hexamer of P4 Protein

• Published in: The Journal of biological chemistry 2003-11, Vol.278 (48), p.48084-48091
• Main Authors: Kainov, Denis E, Pirttimaa, Markus, Tuma, Roman, Butcher, Sarah J, Thomas, Jr, George J, Bamford, Dennis H, Makeyev, Eugene V
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - pharmacology; Amino Acid Sequence; Bacteriophage phi 6 - metabolism; Capsid; Cryoelectron Microscopy; Cystoviridae - metabolism; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; Hydrolysis; Kinetics; Light; Molecular Sequence Data; Neutrons; nucleotide triphosphatase; P4 protein; phage 6; Phage ^H6; RNA - chemistry; RNA - metabolism; RNA Helicases - chemistry; RNA, Double-Stranded - chemistry; RNA, Double-Stranded - metabolism; RNA, Viral - chemistry; Scattering, Radiation; Spectrum Analysis, Raman; Time Factors; Uridine Triphosphate - pharmacology; Virus Assembly
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M306928200

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 φ6 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, φ8 and φ13, were characterized and compared with φ6 P4. All three proteins are hexameric, single-stranded RNA-stimulated NTPases with α/β folds. Using a direct motor assay, we found that φ8 and φ13 P4 hexamers translocate 5′ to 3′ along ssRNA, whereas the analogous activity of φ6 P4 requires association with the procapsid. This difference is explained by the intrinsically high affinity of φ8 and φ13 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.