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Mismatch-specific 3'----5' exonuclease associated with the mitochondrial DNA polymerase from Drosophila embryos
1Department of Biochemistry, Michigan State University, East Lansing 48824.
Abstract:
The mitochondrial DNA polymerase from Drosophila embryos lacks dNTP turnover activity. However, a potent 3'----5' exonuclease activity can be detected by a specific assay in which the exonuclease excises mispaired nucleotides at the 3' termini of primed synthetic and natural DNA templates. The excision of a mispaired nucleotide occurs at a significantly greater rate than excision of a correctly paired nucleotide and, under conditions of DNA synthesis, hydrolysis of a mispaired terminal nucleotide occurs prior to primer extension. The 3'----5' exonuclease copurifies quantitatively with DNA polymerase gamma and cosediments with the nearly homogeneous enzyme under native conditions. These results suggest that the 3'----5' exonuclease provides a proofreading function to enhance the fidelity of DNA synthesis during Drosophila mitochondrial DNA replication.
Insights
Drosophila mitochondrial DNA polymerase has a proofreading exonuclease that removes incorrect DNA bases. This enzyme enhances the accuracy of mitochondrial DNA replication in fruit flies.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Mitochondrial DNA replication requires high fidelity to maintain genomic integrity.
- DNA polymerases often possess proofreading mechanisms to correct errors during synthesis.
Purpose of the Study:
- To investigate the enzymatic activities of Drosophila melanogaster mitochondrial DNA polymerase.
- To determine if this polymerase possesses an intrinsic proofreading capability.
Main Methods:
- Assaying for dNTP turnover and 3' to 5' exonuclease activity using synthetic and natural DNA templates.
- Copurification and cosedimentation studies to assess the association of exonuclease activity with DNA polymerase gamma.
- Characterizing the kinetics of mispaired nucleotide excision versus correctly paired nucleotide excision.
Main Results:
- Drosophila mitochondrial DNA polymerase lacks dNTP turnover activity.
- A potent 3' to 5' exonuclease activity was detected, specifically excising mispaired nucleotides from DNA termini.
- Excision of mispaired nucleotides was significantly faster than correctly paired ones, occurring before primer extension.
- The 3' to 5' exonuclease activity was found to copurify and cosediment with DNA polymerase gamma.
Conclusions:
- The 3' to 5' exonuclease activity associated with Drosophila DNA polymerase gamma functions as a proofreading mechanism.
- This proofreading activity enhances the fidelity of mitochondrial DNA replication in Drosophila embryos.