Gp78 induces convoluted, tubular riboMERCs. Representative whole-cell views of Q95V MERCs (color-coded for increasing size from 500 to 5,613 voxels) from HT-1080 cells, COS-7, or HeLa cells overexpressing Gp78 WT and COS-7 cells overexpressing the OMM–ER linker as well as representative individual Q95V MERCs alone or adjacent to transparent (pink) or solid mitochondria (magenta) to highlight intercalation of riboMERCs with mitochondria. Rotating videos of these MERCs are included as Supplemental Videos 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12. Bar = 1 μm.