Abstract
The structural polypeptides of foot-and-mouth disease virus were digested with Staphylococcus aureus V8 protease in the presence of sodium dodecyl sulfate. The protease-resistant peptides derived from temperature-sensitive mutants were compared with those of the wild type by electrofocusing in a polyacrylamide gel. Covariation between the charge shifts of different peptides indicated that they shared common sequences: only five independent peptides in all were derived from VP1, VP2, and VP3, accounting for approximately 50% of the polypeptide sequences. In two instances, amino acid substitutions that caused similar shifts in the isoelectric point were found to be located in different peptides. However, 15 mutants that possessed identical shifts in VP2 could not be distinguished by peptide analysis. The polypeptides of revertants able to grow at the nonpermissive temperature were compared with those of the parental mutants. By this test, 6 of the 12 distinguishable classes of coat protein mutations were found to covary with temperature sensitivity. In addition to true revertants, several phenotypic revertants which possessed a second charge change, either in a different structural polypeptide or in a different region of the same polypeptide, were isolated. The orientation of the recombination map was deduced from the loci of the coat protein mutations.