Studies on the Morphogenesis of Murine Cytomegalovirus

Two modes of assembly of murine cytomegalovirus (MCMV) were
observed in cultured mouse embryo fïbroblasts, generating two
morphologically different types of viral particles: monocapsid
virions and multicapsid virions. The assembly of nucleocapsids
appeared to be the same for both types of morphogenesis. Three
successive stages of intranuclear capsid formation could be
distinguished: capsids with electron-lucent cores, coreless
capsids, and capsids with dense cores. Some of the capsids were
enveloped at the inner nuclear membrane to form monocapsid virions,
which were first detectable in the perinuclear cisterna. Other
capsids left the nucleus via nuclear pores and usually entered
cytoplasmic capsid aggregates that received an envelope by budding
into extended cytoplasmic vacuoles, thereby forming multicapsid
virions. Since the formation of multicapsid virions is not
restricted to cell culture conditions and also occurs in vivo in
immunosuppressed mice, multicapsid virions may play a role in the
pathogenesis of cytomegalovirus infection.