The structures of turnip crinkle and tomato bushy stunt viruses: II. The surface structure: Dimer clustering patterns

Abstract

Electron microscope images of negatively-stained particles of turnip crinkle and tomato bushy stunt viruses have been analysed. In both cases the particle surface has been shown to consist of 90 morphological units located in the 2-fold positions of the T = 3 icosahedral surface lattice. Such morphological units would then be expected to arise through clustering of the structure units in dimers, making a total of 180 structure units in the protein shell. Smaller particles obtained by degrading turnip crinkle virus have been similarly shown to have 30 morphological units arranged according to the dimer clustering pattern of the T = 1 icosahedral surface lattice. The images of both viruses and of the small particles show extra density in the positions of the 5-fold axes which may either be due to the presence of a second protein component or to clustering of the subunits at an inner radius in these positions.