Intracellular virus DNA distribution and the acquisition of the nucleoprotein core during African swine fever virus particle assembly: Ultrastructural in situ hybridisation and DNase-gold labelling

摘要

The morphogenesis of the attenuated Uganda strain of African swine fever virus (ASFV) was investigated by examining the distribution of intracellular viral DNA in the virus factory and during particle assembly. DNA was localized in infected IB-RS2 cells using a DNA probe specific to the major capsid protein (p73) gene (B646L) hybridized in situ using 2 Lowicryl resins (K4M and HM20) and digoxigenin and biotin as non-radioactive probes, or by detecting viral and cellular DNA with gold-labelled DNase. The results indicate that viral DNA, perhaps from special storage sites within the factory, begins to condense into a pronucleoid and is inserted, at a single vertex, into an 'empty' particle. Closure of the narrow opening in the icosahedron produces an 'intermediate' particle where the nucleoprotein is further consolidated to produce the mature 'full' virions. The site of particle closure may be a weak point at one vertex, but the mechanisms and structures associated with packaging and release of thevirus genome through such a site are unknown.