Fig. 1.

The overall architecture of the MS2/F-pilus complex. a An electron micrograph of the MS2/F-pilus complex. The scale bar denotes 500 Å. b The side view of the MS2/F-pilus complex with the F-pilus colored in orange, the Mat colored in pink, coat proteins in blue, and gRNA in light yellow. For visualization, the density map in Fig. 1 is a composite map with the density of the F-pilus/Mat complex replaced by the 6.2 Å-resolution map, which has a more uniformly well-resolved F-pilus fragment. The axis of the F-pilus is labeled by a horizontal dashed black line with another vertical dashed black line perpendicular to it. A dashed red arrow denotes the two-fold axis on the side of the MS2 capsid. The angle between the vertical dashed black line and the dashed red arrow is 7.8°. c The model of the Mat/F-pilus complex fit in the cryo-EM map. One of the F-pilin is colored from purple (N terminus) to green (C terminus) as in the inset to show the orientation of the F-pilins in the assembled pilus. The three ɑ-helices of an F-pilin are also labeled in the inset. d Cut-in view of the density map of the MS2/F-pilus complex viewed from the direction of the eye cartoon in panel b. The outer and inner diameters of the F-pilus are 87 and 28 Å, respectively. The diameter of the MS2 capsid is ~250 Å. The density of the gRNA is from the refinement of all particles without any mask and low-pass filtered to 8 Å. The inset shows a cartoon model for the asymmetric distribution of the gRNA