The structure of lcosahedral cytoplasmic deoxyriboviruses. II. An alternative model

A detailed comparative ultrastructural study has been made on several icosahedral cytoplasmic deoxyriboviruses (ICDV) of insects and one of vertebrates. The available evidence now seems to indicate that ICDV particles contain only a single structural unit membrane, associated with the viral nucleoid. ICDV shells are therefore redefined entirely in terms of icosahedral lattices, in contrast to an earlier model. A partial explanation is offered for the variability in appearance of ICDV shell surfaces. Previous evidence for the structural relatedness of ICDV's of different sizes and from different hosts is corroborated by the following additional observations: triangular arrays of capsomers (trisymmetrons) are present in mosquito iridescent virus (MIV) shells; mosquito and Corethrella iridescent virus (CoIV) cores are identical in morphology and are uncoated in an apparently intact form under similar conditions; sectioned MIV and frog virus (FV₃) particles reveal definite structural homology; the morphogenesis of all ICDV's studied appears basically identical. Proposals concerning the nomenclature and classification of this group of viruses are briefly discussed.