Fig 2: Interpretation of the cryo-EM structure of human HASt-LTV1 pre-40S particles. (A), The electron density map of HASt-LTV1 pre-40S particles (white density) was fitted with the quasi-atomic 3D structure of the mature human 40S subunit devoid of RPS10 and RPS26 (ribbon style, pale blue unless otherwise stated). The view from the head (left panel) and the close-up of the region framed by a black rectangle (right panel) show that RPS25 in its mature conformation (red ribbon) cannot be fitted in the pre-40S density map. (B), Ribosome biogenesis factors associated to HASt-LTV1 pre-40S particles were positioned on the human pre-40S 3D structure according to CRAC data (8,34) and cryo-EM structures (10,25) obtained in yeast. Segmentation of the HASt-LTV1 pre-40S map was performed with the ‘Segger’ command (75) from Chimera (33). Available atomic models of ribosome biogenesis factors were fitted into their corresponding densities zones by rigid body docking. (C), As a comparison, the electron density map of yeast Rio2-TAP pre-40S particle (EMDB accession code: 1927) was aligned to the human HASt-LTV1 pre-40S particle, by using the ‘Fit’ command of Chimera. The density zones attributed to pre-ribosomal factors are displayed in similar colors in (B) and (C).