Expression of myc- or green fluorescent protein (GFP)-tagged GTPBP8 (Figs. 1A, B, and S2A, B) in human osteosarcoma cells (U2OS) displayed a similar intracellular distribution, co-localizing with the mitochondrial proteins TOM20 and COXIV (Fig. 1A). Here, COX4I1 is linked to osteosarcoma.