Foot-and-mouth disease virus (FMDV), of the Picornaviridae family, is a non-enveloped, single-stranded, positive-sense RNA virus. FMDV infects cloven-hooved animals and is an important pathogen for global agriculture due to the economic consequences of both endemic disease and epidemic outbreaks. In infected cells, production of new FMDV particles involves packaging the genome into an icosahedral capsid assembled from sixty protomeric subunits, but detailed mechanisms for these events are not known and are the subject of investigation in this thesis.
Host-proteins, such as heat-shock proteins (HSPs), have been previously found to enable the proteolytic processing and multimerisation of capsid precursors during the early stages of assembly. An unbiased approach was utilised here to identify various host-proteins interacting with the capsid precursors during each major stage of assembly, and from this a more complete model for capsid assembly was generated where HSP70 binds to unprocessed capsid precursors to enable processing, HSP90 binds the protomer to refold it into a form suitable for multimerisation, and interactions between capsid proteins and host-proteins involved in the replication complex localise the capsid with newly synthesised RNA for encapsidation.
A trans-encapsidation assay was also developed which made it possible to test the effects of mutations in the FMDV genome on RNA encapsidation. Using this assay, it was shown that previously identified putative packaging signals (PPS) dispersed across the genome were required for wt levels of encapsidation, and that mutating these regions impaired encapsidation. Deletion of the 5’-most PPS proved lethal to the virus, and it is demonstrated here that this PPS is an important packaging signal. These packaging signals are predicted to facilitate assembly of the capsid from pentamers recruited to the replication complex by providing a nucleus for pentamers to assemble around, effectively providing a scaffold for capsid assembly which also provides specificity for genome packaging.