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Methods for the three-dimensional reconstruction of icosahedral particles, such as spherical viruses, from electron micrographs are well established. These methods take advantage of the 60-fold symmetry of the icosahedral group. Several features within these particles, however, may deviate from icosahedral symmetry. Examples include viral genomes, symmetry mismatched vertex proteins, unique DNA packaging vertices, flexible proteins, and proteins that are present at less than 100% occupancy. Such asymmetrically distributed features are smeared in the final density map when icosahedral symmetry is applied. Here, we describe a novel approach to classifying, analysing, and obtaining three-dimensional reconstructions of such features. The approach uses the orientation information derived from the icosahedral orientation search to facilitate multivariate statistical analysis and to limit the orientational degrees of freedom for reconstruction. We demonstrate the application of this approach to images of Kelp fly Virus. In this case, each virion may have two different types of fivefold vertex. We use our approach to produce independent reconstructions of the two types of vertex.

Two nodaviruses, both isolated from New Zealand scarab beetles, replicated in DSIR-HA-1179 (HA) cells derived from the black beetle, Heteronychus arator (Coleoptera: Scarabaeidae). Black beetle virus and Flock House virus, isolated from the grass grub (Costelytra zealandica) produced a characteristic cytopathic effect in cells. Virus replication was demonstrated by showing viral RNA synthesis in infected cells. A comparison between HA cells and cells derived from Drosophila melanogaster (line 1) showed that the Drosophila cells were twice as sensitive for detecting black beetle virus and 5 times as sensitive for detecting Flock House virus. Replication of Flock House virus in Drosophila cells was more rapid and more productive than in HA cells.