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Processive DNA synthesis by DNA polymerase II mediated by DNA polymerase III accessory proteins
C A Bonner1, P T Stukenberg, M Rajagopalan
1Department of Biological Sciences, University of Southern California, Los Angeles 90089-1340.
The Journal of Biological Chemistry
|June 5, 1992
Summary
Accessory proteins significantly enhance DNA polymerase II (pol II) processivity, increasing it 150- to 600-fold. These proteins, along with SSB, are crucial for pol II
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Escherichia coli DNA polymerase II (pol II) activity is known to be stimulated by DNA polymerase III (pol III) accessory proteins, specifically the beta,gamma complex.
- Processive DNA synthesis by DNA polymerases is essential for efficient genome replication and repair.
Purpose of the Study:
- To elucidate the mechanism by which the beta,gamma complex stimulates pol II activity.
- To investigate the role of these accessory proteins in DNA lesion bypass by E. coli DNA polymerases.
Main Methods:
- Enzyme kinetics assays were performed to measure DNA synthesis rates and processivity.
- Site-specific abasic lesions were used to assess the bypass capabilities of DNA polymerases I, II, and III in the presence and absence of accessory proteins.
Main Results:
- The beta,gamma complex and SSB protein dramatically increase pol II processivity by 150- to 600-fold, from ~5 to >1600 nucleotides per binding event.
- While pol II's intrinsic synthesis velocity remains unchanged (20-30 nt/s), its overall replication rate is significantly enhanced by accessory proteins.
- Pol II demonstrates limited bypass of abasic lesions, which is dependent on the beta,gamma complex and SSB protein, unlike pol I and pol III.
Conclusions:
- Accessory proteins primarily enhance pol II function by significantly boosting its processivity, not its intrinsic catalytic rate.
- The beta,gamma complex and SSB are essential for pol II-mediated bypass of abasic lesions, highlighting a specialized role in DNA repair.
- While pol III holoenzyme is faster overall, pol II with accessory proteins exhibits a unique capability for lesion bypass, suggesting distinct roles in DNA metabolism.