The fidelity of human DNA polymerase gamma with and without exonucleolytic proofreading and the p55 accessory subunit

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Mutations in mitochondrial DNA (mtDNA) are linked to aging, neuromuscular disorders, metabolic diseases, and apoptosis suppression.
• The genetic stability of mtDNA relies on the accuracy of human DNA polymerase gamma (pol gamma).

Purpose of the Study:

• To investigate the fidelity of DNA synthesis by human pol gamma.
• To understand the mechanisms underlying pol gamma's accuracy and potential error generation.

Main Methods:

• Comparison of wild-type pol gamma with its exonuclease-deficient mutant.
• Analysis of base substitution, single-base addition/deletion, and frameshift fidelity.
• Investigation of pol gamma's fidelity on homopolymeric sequences.
• Assessment of the effect of the p55 accessory subunit on pol gamma fidelity.

Main Results:

• Human pol gamma demonstrates high base substitution fidelity due to nucleotide selectivity and proofreading.
• Pol gamma exhibits relative accuracy for single-base insertions/deletions in non-repetitive sequences.
• Pol gamma shows low frameshift fidelity and generates base substitutions in homopolymeric sequences longer than four nucleotides, likely via a primer dislocation mechanism.
• The p55 accessory subunit decreases both frameshift and base substitution fidelity, promoting extension of mismatched termini.

Conclusions:

• Human pol gamma possesses high fidelity for base substitutions and moderate accuracy for small insertions/deletions.
• Homopolymeric sequences in mtDNA may be susceptible to frameshift mutations due to pol gamma's replication errors.
• The p55 subunit's role in reducing fidelity suggests a complex regulatory mechanism for mtDNA replication accuracy.