Dwight Anderson, Shelley Grimes, and Paul Jardine, Investigators

IMV investigators Dwight Anderson, Shelley Grimes, and Paul Jardine are investigating viral assembly and the description of biological motors at the molecular level. Both historically and experimentally, bacteriophages provide a perfect system to address both of these issues.

A molecular motor assembles transiently to the phi29 prohead capsid and packages DNA to near crystalline density, powered by ATP hydrolysis. The 174-base bacteriophage phi29 prohead RNA (pRNA) is essential for invitro packaging of the 19-kilobase pair DNA-gp 3 complex (DNA-g3) into the viral precursor capsid (prohead). pRNA is an integral part of the phi29 DNA packaging motor, one of the strongest molecular motors characterized, pRNA forms a novel cyclic hexamer by intermolecular base pairing of identical molecules. This multimer binds to the head-tail connector of the prohead, the core of the packaging motor, where it appears as a pentameric ring by cryoEM 3-D reconstruction.

A multimer of the packaging ATPase gp16 then binds the pRNA to complete the motor. pRNA is hypothesized to function in docking of the DNA-gp3 and the prohead, in recognition of the left end of DNA-gp3 to initiate packaging, and as a component of the DNA translocating ATPase. pRNA exits the DNA-filled head during neck and tail assembly, and it is not a part of the mature virion.

Study of the structure and function of this RNA-dependent DNA packaging motor may have general significance for assembly of other viruses, including mammalian viruses.