The morphogenesis of Theiler's murine encephalomyelitis virus is strain specific

During a single cycle infection with the neurovirulent GDVII- and demyelinating DA-strain of Theiler's murine encephalomyelitis virus (TMEV) in L-929 cells, different subviral particles were found for both strains. Early in the assembly process, the DA-strain generated 14 S pentamers composed of the viral proteins VP0, VP1 and VP3, while in GDVII-infected cells, particles with the same protein composition but with a sedimentation coefficient of 20 S were found. These newly discovered 20 S particles are probably virion assembly precursors considering their capsid protein composition and their early time of appearance in infected cells. Near the end of the assembly process, VP0, VP1 and VP3 containing 80 S empty capsids became apparent in GDVII-infected cells, while these particles could not be found in DA-infected cells. The significance of these empty capsids will be discussed. After virion assembly, 14 S particles were observed for both strains. These 14 S particles resulted from the degradation of the 160 S virions as indicated by their protein composition (VP1, VP2, VP3) and time of appearance. Our results demonstrate that the assembly of the GDVII-strain differs from that of the DA-strain. In addition, the strain-specific assembly of TMEV implies that not all picornaviruses assemble as proposed by the poliovirus morphogenesis model and thus rendering its general validity questionable.