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. 2008 Oct;17(10):1731–1739. doi: 10.1110/ps.036905.108

Figure 3.

Figure 3.

Comparison of the wild-type subunit arrangement in MS2 virions to the CCPD subunits in F432 crystal. (A–C) Comparison of the coat protein dimer arrangement in the wild-type icosahedral particles (A) to the packing of CCPD subunits in the octahedral “particles” (B,C). Edges of the triangular faces of the icosahedron (A) and the octahedron (B,C) are shown as black lines together with the positions of the rotation axes. Individual protein chains are rainbow colored from the N terminus in blue to the C terminus in red. The icosahedral asymmetric unit (A) consists of the three subunits A, B, and C. There are two positions for a subunit dimer in the icosahedral arrangement and a CCPD subunit in the octahedral arrangement (compare A to B and C). Since the CCPD subunits have an approximate twofold symmetry, each dimer position can be occupied by two alternative orientations of the CCPD subunit. The region of the icosahedral AB dimer is in the octahedral arrangement occupied by CCPD subunits J or K where the two halves (corresponding to two wild-type subunits) have different structures. The region of the wild-type CC dimer is occupied by the CCPD subunit L. Since the L subunit is positioned on the true twofold rotation axis, the two halves (corresponding to the wild-type subunits) have identical structures except for the linker region and the N and C termini. The twofold rotation axis positions another copy of the L subunit on top of itself (compare B and C). (D) Scheme of the organization of the CCPD subunits in the F432 unit cell. Subunits J, K, and L from three asymmetric units composing one triangular face of the T = 3 octahedron are shown. The length of the edge of the unit cell shown in red is 220 Å. Parts of the subunits J and K that correspond to the subunit A are colored in blue, parts corresponding to the B subunit in red. Subunit L, which is equivalent to the dimer of C subunits, is shown in green. This coloring was used to make the comparison to the wild-type particles easier. (E) Octahedral assembly of CCPD subunits superimposed on an octahedral wire frame. The 24 asymmetric units from the F432 crystal architecture form the octahedral “particles.” CCPD subunits are colored as in D. (F) Model of a wild-type MS2 T = 3 virion superimposed on an icosahedral wire frame. The A subunits are shown in blue, B in red, and C in green. Panels E and F are in scale to allow size comparison.