Fig. 3.

Magnified views of the CA region within the black rectangles in Fig. 2. (A) As in Fig. 2, but focused on CA-NTD. The ordered loop (red arrowhead) between helices 4 and 5 and the C-terminal end of helix 7 (black arrowhead) form the immature CA-NTD dimeric interface. A faint additional density (black arrow) is observed within the central pore of mature CA-NTD hexamer structure. Black hexagon indicates the sixfold axis. (B) As in A, but focused on CA-CTD. The densities marked with asterisks correspond to the immature CA-CTD dimer interface formed by 3₁₀b. Black arrowhead indicates the 3₁₀b helix, and black arrow indicates helix 9. The features illustrated in this figure are also shown in Movie S1, in which the reader may find the spatial relationships easier to visualize. The equivalent views of the mature pentamer are shown in SI Appendix, Fig. S3D.