Figure 4.

Transformation at the hinge. (A) P1_B subunits (red and yellow) are tightly connected to P1_A subunits (blues) of the inverted vertices in the procapsid. This shell contains cavities between the P1_B and P1_A subunits (arrows). (B) In the nucleocapsid, the P1_B subunits are rotated so that the planes of these flat molecules concide with the tangential plane of the shell, leaving no significant cavities between the subunits. (C) Orientation of P1_B subunits (red and yellow ribbons) on either side of a 2-fold icosahedral axis in the procapsid. The subunit planes are almost perpendicular to each other, and their helix-turn-helix motifs are aligned with the 2-fold axis (arrows). (D) Corresponding representation of two P1_B subunits in the nucleocapsid. The two subunits are now almost coplanar. (The views shown in C and D are rotated around the 2-fold axis so that the dihedral angles appear considerably larger.) See also Movie S2.