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Nucleotide excision by E. coli DNA polymerase I in proofreading and non-proofreading modes
1Institut Jacques Monod, Paris, France.
Biochimica Et Biophysica Acta
|December 20, 1988
Summary
Escherichia coli DNA polymerase I exhibits two kinetic forms, switching between low-accuracy and high-accuracy modes. This DNA polymerase proofreading mechanism links fidelity and processivity during DNA synthesis.
Area of Science:
- Molecular Biology
- Biochemistry
- Enzymology
Background:
- Escherichia coli DNA polymerase I is crucial for DNA replication and repair.
- The enzyme possesses both polymerase and 3' to 5' exonuclease (proofreading) activities.
- Understanding the interplay between these activities is key to DNA fidelity.
Purpose of the Study:
- To investigate the distinct kinetic forms of Escherichia coli DNA polymerase I.
- To elucidate the relationship between polymerase processivity and proofreading competence.
- To re-examine the 'warm-up' phenomenon of proofreading activity.
Main Methods:
- Kinetic analysis of DNA synthesis and primer hydrolysis.
- Characterization of enzyme behavior with varying primer lengths.
- Investigation of enzyme processivity and fidelity under different conditions.
Main Results:
- Escherichia coli DNA polymerase I operates in at least two kinetic forms.
- Proofreading is initially off-site upon template binding and becomes competent during synthesis.
- A novel low-accuracy mode involves primer hydrolysis without proofreading, followed by high-accuracy synthesis.
Conclusions:
- The enzyme's proofreading function is reinterpreted as a switch between two modes.
- Mode 1: Active exonuclease uncoupled from polymerase, leading to low accuracy.
- Mode 2: Exonuclease kinetically linked to polymerase, ensuring high accuracy and fidelity.