The picornaviruses are a family of small positive sense single stranded RNA viruses that cause a wide range of diseases at an annual cost well into the hundreds of million dollars. Members include acute hepatitis A virus, the heart disease causing coxsackie B3 virus, rhinoviruses that cause more than half the occurrences of the common cold, and the paralyzing poliovirus. These viruses share a common life cycle where their RNA replication and viral assembly occurs in large membrane anchored replication complexes assembled on the surfaces of vesicles derived from the endoplasmic reticulum. The replication process is driven by a virally encoded RNA dependent RNA polymerase, the 3Dpol protein, that is responsible the synthesis of all viral RNA. Like all picornaviral proteins, the polymerase is generated by proteolytic cleavage of a single large viral polyprotein. There is mounting evidence in several picornaviruses that the polymerase and its immediate precursors are directly responsible for the assembly of these replication centers.

The 3Dpol polymerase of poliovirus, the best studied of the picornaviruses, has been shown by to assemble into large sheet structures along a protein-protein interface that was initially identified in a partial crystal structure of 3Dpol. Mutations that disrupt this interface also disrupt viral RNA binding and synthesis in vitro and affect viral viability in vivo, indicating that this interaction is important for proper viral replication.

The immediate precursor of 3Dpol, the 3CDpro protease, has recently been implicated as a master control molecule responsible for the initiation of both negative and positive strand viral RNA synthesis. 3CDpro forms three specific complexes with RNA secondary structures at different stages of the viral replication process, but the protein has no polymerase activity whatsoever. The molecular basis for this is not yet understood. Also, it is not known if 3CDpro oligomerizes along the same protein-protein interface as 3Dpol to assemble the viral replication complexes.

Using a novel method of intentionally disrupting a known and persistent crystal packing interaction along this interface, we have solved the crystal structure of the complete poliovirus polymerase at 2.0 Å resolution. The structure shows that the very N-terminus of the protein is buried in the structure and that hydrogen bonds to the buried terminus are directly responsible for positioning a key residue in the polymerase active site. This structure is described in our recent EMBO Journal paper.

Structural basis for proteolysis dependent activation of the poliovirus RNA-dependent RNA polymerase (2004). Aaron A. Thompson and Olve B. Peersen EMBO J (2004) Advance online publication.

Self-association of the yeast nucleosome assembly protein 1. Steven J. McBryant and Olve B. Peersen Biochemistry (2004) 43(32):10592-10599.