VIRUS ASSEMBLY IN HINCKSIA-HINCKSIAE (ECTOCARPALES, PHAEOPHYCEAE) AN ELECTRON AND FLUORESCENCE MICROSCOPIC STUDY

The filamentous brown alga Hincksia hincksiae can be infected by a lar ge icosahedral double-stranded DNA virus (HincV-1). The virus shows ex tended latency and is replicated only in cells homologous to sporangia . Virus formation was studied by transmission electron microscopy, DAP I staining, and beta-tubulin immunofluorescence. Inhibition of cytokin eses results in multinucleate cells, which are the first indication of virus replication in productive cells; the microtubular cytoskeleton does nor seem to be affected by the virus. Replication of viral DNA be gins in the nuclei, which increase in size and eventually disintegrate . Virus assembly takes place in a mixed nucleo-/cytoplasm. Capsids bud from cisternae, which are interpreted as modified endoplasmic reticul um aggregated to virus assembly centres. The internal membranous compo nent of the virus is thus derived from the endoplasmic reticulum. The particles are empty (electron translucent) when assembled, and the nuc leoprotein core seems to be packaged subsequently through an opening i n the capsid. A number of fine structural features not previously repo rted from brown algae and related to virus formation are described. Ou r results on Hincksia hincksiae virus are compared with observations m ade on various other icosahedral DNA viruses infecting eukaryotic alga e and animals.