Cryo-electron microscopy image reconstruction of class1, 2, and 3 as obtained by maximum likelihood 3D-classification of psoralen UV crosslinked and heated virions viewed down a 2-fold axis.

<p>(a)–(c), radially color-coded volumes obtained on 3DR imposing icosahedral symmetry (upper half) or without imposing symmetry (lower half); (d) and (f), transverse central sections; (e) for better appreciation of the internal rod-like density, the particle was cut open at about 6 nm above the center of the virion; (g)–(i), central slabs (∼3.8 Å thick); in (e) and (j)–(l), class2 particles are shown with an arrow along the longitudinal axis of the rod indicating the orientation of the internal density with respect to the icosahedral symmetry. Note that the views are on different 2-fold axes. Rotation of the model (k) by 180° around the y-axis indicates that the ‘rod’ contacts the inner face of the virion shell at positions close to a 2-fold and a 3-fold axis at roughly opposite sides. All volumes are depicted with sigma = 1 above the mean density. In (h) the positions of 2-fold (red arrow), 3-fold, and 5-fold axes are indicated. In (a), an obvious deviation from symmetry is indicated with a small black arrow.