TP53 (p53) directly stimulates transcription of the SCO2 gene. SCO2, synthesis of cytochrome c oxidase 2, is a copper-binding assembly protein for the mitochondrial COX (cytochrome C oxidase) complex which enables aerobic respiration. When SCO2 levels are reduced, as occurs in TP53 deficient cells, the glycolysis becomes the main energy source for the cell. The TP53-mediated regulation of SCO2 and other mitochondrial biogenesis genes provides a possible explanation for the Warburg effect (Warburg 1956) observed in some cancer cells (Matoba et al. 2006).