Figure 2.
Movement of the 30S Head Widens the mRNA Entry Channel and Opens the Latch
(A) Front view of the orientation of the 30S head in PIC-1C (yellow), PIC-2B (blue), and PIC-4 (red), using the 30S body for alignment. The displacement of the beak in the three PICs highlights the difference in the orientation of the head. The P-site tRNA is shown. The top view shows the rotation axis of the head around h28. The magnitudes of the changes are shown using C1030b as the reference point.
(B) Front view of superposition of refined models of PIC-1C (yellow), PIC-2B (blue), and PIC-4 (red) indicating elements forming the latch. The movement of 12 Å of A1001 in the 30S head is shown. Bottom panel: surface representation of PICs 1C, 2B, and 4, with the arrows indicating the opening and closing of the mRNA latch.
(C) The conformation of h28 in PIC-1C (yellow), PIC-2B (blue), and PIC-4 (red). Equivalent atoms in h28 (C1384) are shown as spheres. In PIC-1C, h28 is not compressed, and the mRNA latch is open. The opposite is seen in PIC-4. In PIC-2B, the mRNA latch is closed by a head swivel rather than compression of h28.