title: DNA oxidation by charge transport in mitochondria.
abstract: Sites of oxidative DNA damage in functioning mitochondria have been identified using a rhodium photooxidant as a probe. Here we show that a primer extension reaction can be used to monitor oxidative DNA damage directly in functioning mitochondria after photoreaction with a rhodium intercalator that penetrates the intact mitochondrial membrane. The complex [Rh(phi)2bpy]Cl3 (phi = 9,10-phenanthrenequinonediimine) binds to DNA within the mitochondria and, upon irradiation, initiates DNA oxidation reactions. Significantly, piperidine treatment of the mitochondria leads to protein-dependent primer extension stops spaced every approximately 20 base pairs. Hence, within the mitochondria, the DNA is well covered and packaged by proteins. Photolysis of the mitochondria containing [Rh(phi)2bpy]3+ leads to oxidative DNA damage at positions 260 and 298; both are mutational hot spots associated with cancers. The latter position is the 5'-nucleotide of conserved sequence block II and is critical to replication of the mitochondrial DNA. The oxidative damage is found to be DNA-mediated, utilizing a charge transport mechanism, as the Rh binding sites are spatially separated from the oxidation-prone regions. This long-range DNA-mediated oxidation occurs despite protein association. Indeed, the oxidation of the mitochondrial DNA leads not only to specific oxidative lesions, but also to a corresponding change in the protein-induced stops in the primer extension. Mitochondrial DNA damage promotes specific changes in protein-DNA contacts and is thus sensed by the mitochondrial protein machinery.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Merino
authors.forename: Jacqueline K
authors.initials: JK
authors.lastname: Barton
mesh_terms: D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004587:Electrophoresis, Agar Gel; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D004247:DNA