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.