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The structure of the protein shell of turnip yellow mosaic virus

1960; Elsevier BV; Volume: 2; Issue: 4 Linguagem: Inglês

10.1016/s0022-2836(60)80036-8

1089-8638

H. E. Huxley, Geoffrey Zubay,

Bacteriophages and microbial interactions

Turnip yellow mosaic virus (TYMV) is an approximately spherical plant virus, having a diameter of 280 to 300 Å and containing 60% protein and 40% RNA; the protein is believed to form a spherical shell around a nucleic acid core. It has been shown previously by X-ray diffraction that the virus particles must have cubic symmetry, and it has been argued on theoretical grounds that viruses having cubic symmetry and containing a spherical shell of protein were likely to have that protein shell built up of subunits arranged in a polyhedron having either tetrahedral (23), octahedral (432) or icosahedral (532) symmetry elements. We have examined TYMV in the electron microscope by the negative staining method, and have found that regularly disposed subunits may be discerned on the surface of the particles. There appear to be 32 such subunits, arranged on or near the vertices of either a pentakis dodecahedron or a rhombic triacontahedron (or other polyhedra approximating to those forms). These are semi-regular poly-hedra having 532 symmetry, the former having 60 identical triangular faces and the latter 30 identical rhombic faces; both have 32 vertices, which fall into two separate groups, 12 vertices lying on fivefold axes and 20 vertices lying on threefold axes. Thus the subunits occupy two different types of position, and can be of two different species. Because the subunits lie on rotation axes, they must contain the appropriate number of identical structural units. These results agree with the suggestion made on the basis of the X-ray results that the particles have 532 symmetry, but they conflict with the more tentative suggestion that the particular polyhedron involved contained 60 subunits placed at the vertices of a snub dodecahedron. A possible way in which the X-ray results can be reconciled with the present observations is suggested.