Temperature-sensitive mutants of foot-and-mouth disease virus with altered structural polypeptides. I. Identification by electrofocusing

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Abstract
The structural polypeptides of foot-and-mouth disease virus were analyzed by electrofocusing in a polyacrylamide gel containing 9 M urea. Three versions of the technique were used to accommodate the widely differing isoelectric points of the 4 polypeptides. VP2 was identified by comparing mature virus with procapsids. The selective actions of proteases on virions of 2 serotypes and on their 12S particles were examined. From this emerged a simple test for distinguishing the similarly sized polypeptides: VP1, VP2 and VP3. The effects of carbamylation and succinylation on the charge of the polypeptides were investigated. Analysis of the properties of polypeptides modified chemically or by mutation showed that all amino acid substitutions expected to cause a charge change are detected except for neutral-to-histidine substitutions in the most basic polypeptide, VP1. In 73 temperature-sensitive mutants, 11 classes of variant polypeptides were distinguished on the basis of charge. Their MW were unchanged. Alterations were found in all structural polypeptides except VP4. Mutations affecting VP2 caused similar shifts in the precursor, VP0.