Wolf, S, Maier, I, Müller, DG
Fakultät für Biologie der Universität, D-78457 Konstanz, Germany
The filamentous brown alga Hincksia hincksiae can be infected by a large icosahedral double-stranded DNA virus, HincV-1. The virus is latently present in somatic cells of the host and is replicated only in the presumptive reproductive cells. Virus formation was studied by DAPI staining, tubulin immunofluorescence and transmission electron microscopy. The first indication of infection is a lack of cytokineses in the virus producing cells resulting in multinucleate cells, whereby the microtubular cytoskeleton does not seem to be affected. Replication of viral DNA begins in the nuclei, which increase in size and eventually disintegrate. Capsid formation starts in the cytoplasm, maturation of the virus particles takes place in a mixed cyto-/nucleoplasm after nuclear breakdown. Capsids bud from the edge of cisternae which are possibly modified ER aggregated to virus assembly centres. The internal membrane of the capsid is thus derived from the ER. When assembled the particles appear empty, the nucleoprotein core seems to be packaged subsequently through an opening in the capsid. Several fine structural features related to virus formation are described. A comparison is made with other brown algal host-virus systems.