UQCC3 is a mitochondrial inner membrane protein essential for assembly and stabilization of respiratory complex III (cytochrome bc1 complex), functioning downstream of assembly factors UQCC1 and UQCC2 1. The protein mediates cytochrome b recruitment and stabilization within the complex, thereby supporting mitochondrial ATP production 2. UQCC3 binds cardiolipin through its α-helices 2 and 3, regulating cardiolipin composition and cristae morphology 2. Beyond its canonical respiratory function, UQCC3 orchestrates mitochondrial bioenergetics by forming a positive feedback loop with reactive oxygen species to coordinate OXPHOS and glycolysis, particularly under hypoxic stress 3. Clinically, loss-of-function mutations in UQCC3 cause mitochondrial complex III deficiency (nuclear type 9), presenting with severe multisystem manifestations including lactic acidosis, hypoglycemia, hypotonia, and developmental delay 1. Complex III deficiency frequently manifests as combined respiratory chain dysfunction affecting complexes I and IV, suggesting UQCC3's role in supercomplex stabilization 4. Emerging evidence links reduced UQCC3 expression to malignant hyperthermia susceptibility, suggesting involvement in skeletal muscle mitochondrial dysfunction 5. Additionally, UQCC3 functions as an interferon-independent antiviral protein through OAS3-RNase L pathway activation 6, expanding its biological roles beyond energy metabolism.