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SUMMARY The polypeptides of several strains of the seven serotypes of foot-and-mouth disease virus have been examined by polyacrylamide gel electrophoresis. Most strains gave a distinctive pattern of separation in urea-polyacrylamide gels but all the viruses contained one polypeptide which migrated to the same position. The mol. wt. of this polypeptide (VP 4) was shown by co-electrophoresis in sodium dodecyl sulphate-polyacrylamide gels to be the same, 13.5 × 103, for all seven serotypes. Since VP 4 aggregates when it is dissociated from the virus, it can be separated readily from acid-disrupted virus particles by centrifuging. It has the properties of a group antigen since it reacts in complement fixation tests with both homotypic and heterotypic antisera. The reaction between VP 4 and heterotypic antisera has also been demonstrated by using 125I-Fab fragments. The antigenic site of VP 4 is not located on the surface of virus particles since there is no reaction between intact particles and 125I-labelled heterotypic IgG or its Fab fragments.
Talbot et al. (1973) studied this question.