TACO1 (translational activator of cytochrome c oxidase I) is a mitochondrial protein that functions as a translational regulator of oxidative phosphorylation (OXPHOS) components. Primary function: TACO1 acts as a translational activator specifically for mitochondrially-encoded cytochrome c oxidase subunits (COX1 and COX3) 1. Mechanism: TACO1 alleviates mitoribosome stalling at polyproline-rich stretches within COX1 and COX3 mRNAs by cooperating with ribosomal subunit bL27m to stabilize the peptidyl-transferase center 1. The protein functions as a general post-initiation mitochondrial translation factor 2, and its stability is maintained through interaction with the chaperone PET117, which prevents TACO1 ubiquitination 3. Disease relevance: TACO1 mutations cause Leigh syndrome with complex IV deficiency 1, with viral infections exacerbating this phenotype 4. Proteomic analysis revealed TACO1 downregulation in myotonic dystrophy type 2 muscle 5. Clinical significance: TACO1 is upregulated in bladder and gastric cancers, where elevated mitochondrial TACO1 drives chemoresistance and stemness through OXPHOS enhancement and reactive oxygen species production, and associates with poor prognosis 67. Physical activity increases TACO1 expression, suggesting a mechanism for exercise-mediated mitochondrial health 8.