Focused 3D classification and refinement of the platform domain of Tsr1-FPZ pre-40S particles. (a) Structural details of 3D class P1, solved to 3.7 Å resolution. The full cryo-EM map of this region is displayed. Rps1 is shown in light green, Rps14 in violet, Dim2 in orange. Other ribosomal proteins are shown in light blue ribbons in white electron densities, while rRNA is shown in light grey, with the exception of its 3′-end region, displayed in dark grey. (b) Structural details of 3D class P2, refined to a resolution of 9.1 Å. Like for P1, all the electron densities of the cryo-EM map are displayed and color codes are identical to P1.