A NEW MITOCHONDRIAL ENZYME, INVOLVEMENT IN MITOCHONDRIAL DNA REPLICATION AND GENETIC DISEASE

Mutations in mitochondrial DNA are detrimental due to the key function of mitochondria in energy metabolism and cell death. Many human diseases are in fact caused by mitochondrial abnormalities. Mitochondrial DNA replicates independently of nuclear DNA but, like the latter, during replication it needs appropriate and balanced amounts of its four precursors (the dNTPs). Inside the cell the dNTP concentrations are controlled not only by biosynthetic enzymes but also by degradative enzymes that avoid dNTP imbalances. We have recently discovered a new degradative enzyme (a deoxynucleotidase, dNT-2) working inside mitochondria. This is the first known mitochondrial deoxynucleotidase and we want to study its biologic function because several indications point to its importance for preventing mitochondrial DNA mutations and the diseases they may cause. Furthermore, we have discovered that in humans the gene for dNT-2 maps on chromosome 17 in the region deleted in the Smith-Magenis syndrome (SMS). Such region encompasses several known genes, but it is still unclear if one of them is the main responsible for the syndrome. Aim of our work is also to assess if the new gene contributes to the SMS. We will pursue our aims as follows: 1) we will prepare model systems (genetically modified cells and mice) and analyze them by biochemical, molecular and cellular methods in order to recognize the influence of the gene on mitochondrial function; 2) we will look for mutations in the dNT-2 gene in patients with mitochondrial genetic abnormalities of unknown ethiology and measure dNT-2 enzymatic activity in cells from patients affected by SMS and other mitochondrial diseases.