ABSTRACT
Foot-and-mouth disease virus encodes all of its proteins in the form of a polyprotein. The full-length translation product (some 2,330 amino acids) is not observed within infected cells, however, due to processing of the polyprotein. The polyprotein undergoes three co-translational, intramolecular, or ‘primary’, cleavages mediated by the virus-encoded proteinases L and 3C, and a short oligopeptide sequence (2A). 2A-mediated ‘cleavage’ is now thought to be a translational effect: an unusual ribosome ‘skipping’ activity. The polyprotein primary cleavage products then undergo ‘secondary’ proteolytic processing by a combination of inter- and intramolecular cleavages to produce the mature processing products. The aphthoviruses are unique in possessing a proteinase (Lpro) at the N-terminus of the polyprotein. The L and 3C proteinases serve not only to cleave the virus polyprotein, but to degrade certain host-cell proteins thereby greatly enhancing virus replication. The strategy of encoding proteins as polyproteins comprising virus-encoded proteinases lies, therefore, at the core of the replication strategy of these viruses.
