Figure 3.

Shaded-surface representations of 3-fold view of E₂ core. (A) E₁ was removed from PDC to reveal the underlying E₂ core (green) and its inner linkers (light blue). An E₂ trimer is outlined by the yellow square, and the 5-, 3-, and 2-fold axes are indicated. The linkers change the shape of the trimer base so that it appears that they are connected to its corners. (B) Superposition of the cut-away cryoEM PDC structure and the x-ray structure of B. stearothermophilus tE₂. The atomic model of the tE2 dodecahedral core was directly superimposed on the core of the cryoEM structure by aligning the icosahedral 5-, 3-, and 2-fold axes with those of the cryoEM structure. For clarity, only one of the 20 tE₂ trimers of the atomic model is shown. The dark and light blue and green x-ray ribbon structure represent the three identical subunits that comprise the tE₂ core. The three N-terminal linkers are directly opposite the N-terminal helix (H1) near the middle of the outside edge of the trimer base as indicated, and the N-terminal loop is directed toward the 3-fold axis. The bridge interconnects adjacent trimers to form the dodecahedral core.