Here we demonstrate a new conserved role for p53 in mtDNA copy number maintenance and mitochondrial reactive oxygen species (ROS) homeostasis. In mammals, mtDNA is present at thousands of copies per cell and is essential for normal
development and cell function. We show that p53 null mouse and p53 knockdown human primary
fibroblasts exhibit mtDNA depletion and decreased mitochondrial mass under normal culture growth
conditions.