The main criterion for including a virus in this enlarging group of viruses is viral morphology. The unique morphology of herpesviruses was unknown until Wildy et al. (1960) introduced the negative staining technique to electron microscopy. They found that herpes simplex virus did not have the spherical shape thought, up to 1960, to be common to many viruses. In sections prepared by negative staining, the naked virus particle or capsid was shown to be an icosahedron (20-sided body) in shape, containing 162 subunits or capsomeres, with five capsomeres along each edge of the triangular facet of the icosahedron. The capsid of herpes simplex virus had an overall diameter of 105 nm, and the capsomeres were either pentagonal or hexagonal and 10 nm in diameter. Within the hollow capsid was the core, which contained the viral genome. The structure of the core was less well defined by electron microscopy. Surrounding the capsid, some particles, presumably the complete infectious unit, possessed an outer membrane or envelope. This envelope increased the diameter of the complete virion to about 180 nm. It is now known that all viruses belonging to the herpes group share this morphology. The morphology of human CMV (CMV), described by Wright et al. (1964), is illustrated in Fig. 4.1.
KeywordsHeparin Hexagonal Fractionation Polypeptide Thymidine
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