Exonuclease action of replicative polymerase gamma drives damage-induced mitochondrial DNA clearance

Area of Science:

• Mitochondrial Biology
• Molecular Genetics
• DNA Replication and Repair

Background:

• Mitochondrial DNA (mtDNA) replication is crucial for cellular energy production and is performed by DNA polymerase gamma.
• Replication stress, often caused by DNA lesions like oxidative damage, can compromise mtDNA stability.
• The precise mechanisms by which mtDNA lesions impact polymerase activity and genome integrity in vivo remain unclear.

Purpose of the Study:

• To investigate how mtDNA-specific damage affects polymerase activity and mtDNA stability in Saccharomyces cerevisiae.
• To elucidate the mechanisms underlying the clearance of damaged mtDNA.
• To understand the role of DNA polymerase gamma's dual functions in maintaining mitochondrial genome integrity.

Main Methods:

• Induction of mtDNA-specific damage in S. cerevisiae.
• Quantification of mtDNA loss.
• Assessment of mtDNA clearance mechanisms in relation to cell cycle and dNTP levels.
• Analysis of DNA polymerase gamma's 3'-5' exonuclease activity.

Main Results:

• Induced mtDNA damage led to significant mtDNA loss.
• mtDNA loss occurred independently of cell cycle progression or cell division, indicating an active clearance process.
• The 3'-5' exonuclease activity of mtDNA polymerase was implicated in the clearance of damaged mtDNA.
• Cellular dNTP levels influenced the rate of mtDNA loss.

Conclusions:

• Mitochondrial DNA damage triggers an active, cell cycle-independent clearance mechanism.
• The 3'-5' exonuclease activity of polymerase gamma plays a key role in removing damaged mtDNA.
• Cellular dNTP levels modulate the efficiency of damaged mtDNA clearance.
• These findings highlight a context-dependent, selective regulation of polymerase gamma functions to maintain mitochondrial genome integrity.