Ribosome-associated protein import alters the local architecture of the outer and inner mitochondrial membranes. (A) Ribosome and membrane model defining co-translation-associated and non-co-translation-associated patches on membrane surface mesh reconstruction for the OMM–IMM distance measurement. Co-translation-associated patches (blue) included the nearest OMM triangles (black in the middle of blue patch) to the import-oriented ribosomes and the OMM triangles within 150 Å of these nearest OMM triangles. Non-co-translation-associated patches (gray) consisted of the OMM mesh triangles that excluded co-translation-associated patches. (B) Quantification of the peak histogram values of OMM–IMM distance measurements for each tomogram within the indicated membrane patch region. The co-translation-associated and non-co-translation-associated patches are detailed in Fig. 4 A. The “all membrane” patches represent the entire OMM surface. The “randomized” patches were simulated according to the number of co-translation-associated patches, as outlined in Materials and methods. Quantification of CHX-treatment data n = 87 and of vehicle-treatment data n = 18 tomograms are shown. P values from Mann–Whitney U test are indicated. *P < 0.05; ****P < 0.001. (C) Representative membrane surface reconstruction of mitochondria colored by OMM–IMM membrane distance, with regions <10 nm shown in blue and regions >10 nm shown in gray. Ribosomes oriented for import relative to the OMM are colored blue, and the remaining ribosomes near but not oriented for import are shown in pink. Insets show zoomed-in boxed regions of the models (middle) and the local variations in OMM–IMM distance (right).