Related Experiment Video
Updated: Aug 15, 2026
Tools to Study the Role of Architectural Protein HMGB1 in the Processing of Helix Distorting, Site-specific DNA Interstrand Crosslinks
Published on: November 10, 2016
DNA interstrand cross-links induced by psoralen are not repaired in mammalian mitochondria
1Department of Biochemistry, La Trobe University, Bundoora, Victoria, Australia.
Abstract:
Although it is generally known that mitochondria are defective in DNA damage processing, little is known about the DNA repair pathways and mechanisms that exist in these vital organelles. Certain lesions that are removed by base excision repair are efficiently removed in mitochondria, whereas some bulky lesions that are removed by nucleotide excision repair are not repaired in these organelles. There has been much interest in whether mitochondria possess activities for recombination repair, and some previous studies have reported such activities, whereas others have not. We have taken the approach of studying the formation and removal of interstrand cross-links (ICLs) in DNA. These lesions are thought to be repaired by a repair mechanism that involves nucleotide excision and recombinational repair. The formation and repair of DNA ICLs by 4'-hydroxymethyl-4,5',8-trimethylpsoralen was investigated in both the nuclear and mitochondrial genomes in hamster cells. Seven-fold-higher levels of ICLs were generated in mtDNA than in the dihydrofolate reductase gene, clearly indicating that the mitochondrial genome is a preferential target of 4'-hydroxymethyl-4,5',8-trimethylpsoralen damage. ICLs were removed efficiently from the dihydrofolate reductase gene, but no repair was observed in mtDNA. Our observations support previous work showing efficient gene-specific repair of these lesions in the nucleus but suggest that repair of this type of ICL does not exist in the mitochondria. The preferential damage of mtDNA and the absence of cross-link repair further suggests that mtDNA may be a biologically important target for psoralen.
Insights
Mitochondria are preferentially damaged by psoralen, forming interstrand cross-links (ICLs). Unlike nuclear DNA, mitochondrial DNA (mtDNA) lacks repair mechanisms for these ICLs, suggesting mtDNA is a significant target for psoralen toxicity.
Area of Science:
- Mitochondrial biology
- DNA repair mechanisms
- Genotoxicology
Background:
- Mitochondria possess DNA repair pathways, but their completeness and efficiency remain largely unknown.
- While some DNA lesions are repaired in mitochondria, others, like bulky adducts repaired by nucleotide excision repair, are not.
- The existence of recombination repair in mitochondria is debated, with conflicting findings in previous studies.
Purpose of the Study:
- To investigate the formation and repair of DNA interstrand cross-links (ICLs) in both nuclear and mitochondrial genomes.
- To determine if mitochondria possess repair mechanisms for ICLs, which involve nucleotide excision and recombinational repair.
- To assess the susceptibility of mitochondrial DNA (mtDNA) to psoralen-induced damage and its repair capacity.
Main Methods:
- Hamster cells were treated with 4'-hydroxymethyl-4,5',8-trimethylpsoralen to induce DNA interstrand cross-links (ICLs).
- The formation and removal of ICLs were analyzed in both the nuclear genome (dihydrofolate reductase gene) and the mitochondrial genome (mtDNA).
- Quantitative assessment of ICL levels and repair kinetics in both genomic compartments.
Main Results:
- Mitochondrial DNA (mtDNA) sustained seven-fold higher levels of ICLs compared to the nuclear dihydrofolate reductase gene, indicating preferential damage.
- ICLs were efficiently removed from the nuclear dihydrofolate reductase gene, consistent with known nuclear repair pathways.
- No significant repair of ICLs was observed in the mitochondrial genome (mtDNA).
Conclusions:
- Mitochondrial DNA (mtDNA) is a preferential target for 4'-hydroxymethyl-4,5',8-trimethylpsoralen-induced interstrand cross-links (ICLs).
- Mitochondria appear to lack the repair pathways necessary to remove ICLs, unlike the nuclear genome.
- The combination of preferential damage and lack of repair suggests that mtDNA is a biologically significant target for psoralen genotoxicity.
Related Concept Videos
01:36Mismatch Repair
01:08Nucleotide Excision Repair
01:08Nucleotide Excision Repair
01:35Mutations
Chromosomal Alterations Are Large-Scale Mutations
While point mutations are changes in a single nucleotide in...
01:38Nucleotide Excision Repair
Cells are regularly exposed to mutagens—factors in the environment that can damage DNA and generate mutations. UV radiation is one of the most common mutagens and is estimated to introduce a significant number of changes in DNA. These include bends or kinks in the structure, which can block DNA replication or transcription. If these errors are not fixed, the damage can cause mutations, which in turn can result in cancer or disease depending on which sequences are...
01:20Mismatch Repair
The Mutator Protein Family Plays a Key Role in DNA Mismatch Repair
The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic...