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Autonomous 3'-->5' exonucleases can proofread for DNA polymerase beta from rat liver
I V Shevelev1, N V Belyakova, T P Kravetskaya
1Laboratory of DNA Biosynthesis, Division of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute of the Russia Academy of Sciences, Gatchina, Leningrad, Russia.
Mutation Research
|May 17, 2000
Summary
Autonomous 3'-->5' exonucleases significantly enhance DNA polymerase accuracy. These enzymes, found in various organisms, boost fidelity by over tenfold, improving DNA replication accuracy in vitro and potentially in vivo.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Autonomous 3'-->5' exonucleases are crucial for DNA replication fidelity.
- These enzymes are not covalently bound to DNA polymerases but function within replicative complexes.
- Mammalian DNA polymerase beta is known for its low accuracy.
Purpose of the Study:
- To investigate the role of 3'-->5' exonucleases in enhancing DNA polymerase accuracy.
- To quantify the fidelity increase mediated by these exonucleases in vitro.
- To extrapolate in vitro findings to cellular DNA synthesis accuracy.
Main Methods:
- In vitro DNA replication assays using primed bacteriophage phiX174 DNA.
- Utilizing DNA polymerase beta from rat liver and purified 3'-->5' exonucleases from rat liver, calf thymus, and E. coli.
- Varying concentrations of 3'-->5' exonuclease to assess its impact on fidelity.
Main Results:
- 3'-->5' exonucleases increased the accuracy of rat liver DNA polymerase beta by over tenfold.
- The fidelity enhancement correlated directly with increasing concentrations of the exonuclease.
- Results were consistent with primers of different lengths (15 and 150 nucleotides), ruling out primer degradation as the sole mechanism.
Conclusions:
- Exonucleolytic proofreading by 3'-->5' exonucleases significantly augments DNA synthesis accuracy.
- Cellular DNA replication fidelity could be improved by two orders of magnitude through this mechanism.
- This study highlights the critical role of proofreading exonucleases in maintaining genomic integrity.