Related Experiment Videos
'External' proofreading of DNA replication errors and mammalian autonomous 3'-->5'exonucleases
I V Shevelev1, T P Kravetskaya, O K Legina
1Department of Molecular and Radiation Biophysics, Petersburg Nuclear Physics Institute of the Russia Academy of Sciences, Gatchina, Leningrad District, Russia.
Mutation Research
|June 10, 1996
Summary
Mammalian DNA polymerases alpha and beta lack proofreading. Autonomous 3'-->5' exonucleases, found in various rat tissues, likely provide essential external proofreading to correct DNA replication errors.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Mammalian nuclear DNA polymerases alpha and beta lack intrinsic 3'-->5' exonucleolytic proofreading activity.
- DNA base substitutions by these polymerases require external mechanisms for correction.
- Proofreading can be mediated by DNA polymerases delta/epsilon or autonomous exonucleases.
Purpose of the Study:
- To investigate the role and prevalence of autonomous 3'-->5' exonucleases in DNA repair.
- To determine the contribution of autonomous exonucleases to the overall proofreading activity in mammalian cells.
Main Methods:
- Ultracentrifugation of nuclear extracts and cytosols from rat tissues (liver, spleen, brain, heart) and embryos.
- Separation of DNA polymerases delta and epsilon from autonomous 3'-->5' exonucleases.
- Analysis of 3'-->5' exonuclease activity levels in correlation with organ replicative status.
Main Results:
- The majority of cellular 3'-->5' exonucleolytic activity originates from autonomous nucleases, not polymerases delta/epsilon.
- Exonuclease activity levels correlate with tissue replicative rates (spleen > regenerating liver > normal liver > cardiac muscle > brain).
- Autonomous exonucleases are components of DNA polymerases alpha and beta multi-enzyme complexes.
Conclusions:
- Autonomous 3'-->5' exonucleases are the primary mediators of external proofreading in mammalian cells.
- These exonucleases play a crucial role in maintaining genomic integrity by correcting replication errors.
- Their association with DNA polymerases alpha and beta suggests a direct role in DNA synthesis fidelity.