Fish lymphocystis disease is a common viral infection reported in over a hundred teleost species. The causative agent, Lymphocystis disease virus (LDV), has been classified in the Iridoviridae family. Though it has an icosahedral shape, its capsid is complex and still not very well characterized. However, several studies have been reported on the ultrastructure of Frog virus 3 (FV3), another iridovirus, showing outside protein units with an underlying lipidic layer, surrounding the viral core. In order to verify whether or not the structure of LDV particles correspond to that of FV3 , a comparative electron microscopic study was undertaken.LDV strain Leetown (ATCC VR-342) was propagated on BF-2 cells, and FV3 strain Granoff (ATCC VR-567) on FHM cells. Viral particles, concentrated and suspended in 0.1M Tris buffer (pH appropriate for the enzyme used), were adsorbed on formvar-coated grids prior to digestion with proteases (pronase E or proteinase K, 20 U/ml) and/or phospholipases (A2 or C, 15 U/ml) at 37°C for various incubation periods. Particles were negatively stained with 2% (w/v) phosphotungstic acid pH 6.0 before examination with a Philips 300 transmission electron microscope (TEM) at 80 kV.
Cell-free translation of frog virus 3 messenger RNAs. Initiation factors from infected cells discriminate between early and late viral mRNAs.