Needle complex reconstruction and symmetry analysis.

(A) Cross-section and side view of the symmetry-free (C1) reconstruction of the Shigella needle complex. The structural features and their dimensions are indicated. Arrows show the position of the slices shown in panel B. (B) Horizontal slices of the periplasmic IM ring (bottom panel),the connector (middle panel) and the OM ring (upper panel, from non-sharpened map). (C) Rotational autocorrelation analysis of the three slices shown in panel B indicating C24 symmetry for the IM ring (24 peaks spaced by 15 degrees), C16 symmetry for the connector (16 peaks spaced by 22.5 degrees) and C15 symmetry for the OM ring (15 peaks spaced by 24 degrees). A circular mask with inner radius 55 Å and outer radius 76 Å was applied to the OM ring slice to highlight the 15-fold periodicity.