Further characterization of a morphogenetic mutant of the foot-and-mouth disease virus.

In this paper we describe further characterization of a foot-and-mouth disease virus (FMDV) temperature-sensitive mutant, ts 139. This mutant was very sensitive to heat inactivation, suggesting that its viral particles are somehow altered. The electrophoretic analysis of ts 139 structural proteins indicated that VP2 has an altered mobility. Furthermore, two known protein precursors of VP2, VP0 and p88, were shown to be altered, as was p64, which supports a VP2 precursor role for p64. The ts 139 viral particle assembly pathway was analyzed during viral replication. The empty-capsid to complete-viral-particle ratio was clearly increased compared to that found for the wt strain, indicating an alteration in the morphogenetic process. This encouraged us to search for the presence of possible viral precursors of low sedimentation coefficient which have not been described previously in aphthovirus-infected cells. Analysis of the viral morphogenetic process in ts 139-infected cells demonstrated the presence of viral complexes formed by VP0, VP1 and VP3 which sedimented slightly faster than a 12 S marker. The protein composition, the sedimentation coefficient of this complex and the pulse-chase results strongly suggest that it is a morphogenetic precursor of the mature viral particle.