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The structure of turnip crinkle virus has been determined at 3.2 A resolution, using the electron density of tomato bushy stunt virus as a starting point for phase refinement by non-crystallographic symmetry. The structures are very closely related, especially in the subunit arm and S domain, where only small insertions and deletions and small co-ordinate shifts relate one chain to another. The P domains, although quite similar in fold, are oriented somewhat differently with respect to the S domains. Understanding of the structure of turnip crinkle virus has been important for analyzing its assembly, as described in an accompanying paper.

The yeast virus is a double-stranded RNA virus with a large genomic dsRNA and one major viral capsid polypeptide. Most strains of yeast have a major and a minor species of the large genomic dsRNA present. The major species has previously been shown to encode a capsid polypeptide with a Mr of about 88,000. We show that the minor species also encodes its capsid polypeptide with a Mr of about 80,000. Unlike all the dsRNA viruses of procaryotes and higher eucaryotes, the yeast virus appears to have only one major polypeptide in its virions. There are some 60 molecules of this capsid polypeptide per particle, consistent with a simple icosohedron of T=1.

The coat proteins of the leafhopper transmitted gemini viruses, viz., maize streak virus and wheat dwarf virus that contain a single circle of DNA in their genomes are shown to bear good amino acid sequence homology with the coat protein of an RNA plant virus, the satellite tobacco necrosis virus. It is suggested that for icosahedral assemblage, the coat protein architecture transcends genomic preferences.