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Short gap-filling synthesis by DNA polymerase beta is processive
1Sealy Center for Molecular Science, University of Texas Medical Branch, Galveston 77555-0851.
The Journal of Biological Chemistry
|July 25, 1993
Summary
Mammalian DNA polymerase beta (beta-pol) can fill DNA gaps, challenging previous notions. Its gap-filling is processive for short gaps, especially with a 5'-phosphate, suggesting a unique role in DNA repair.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Mammalian DNA polymerase beta (beta-pol) is implicated in DNA repair.
- Previous studies noted limitations in beta-pol's gap-filling and distributive synthesis mechanism.
- Conceptual issues existed regarding beta-pol's complete role in DNA repair.
Purpose of the Study:
- To investigate the gap-filling and gap recognition capabilities of beta-pol.
- To clarify the mechanism of beta-pol's synthesis on gapped DNA substrates.
- To determine if beta-pol exhibits processive or distributive synthesis in gap repair.
Main Methods:
- Designed synthetic DNA substrates with varying gap sizes (1-53 nucleotides).
- Utilized M13mp18(+) single-stranded DNA as a template.
- Employed synthetic deoxyoligonucleotides as primers and downstream polynucleotides.
Main Results:
- Beta-pol demonstrated the ability to completely fill DNA gaps.
- Gap-filling activity for gaps up to 6 nucleotides was highly processive, not distributive.
- Processive synthesis required a 5 phosphate on the 5 moiety of the gap.
- Other DNA polymerases did not show similar specificity for short gap filling.
Conclusions:
- Beta-pol can effectively fill DNA gaps, contrary to prior assumptions.
- The mechanism involves processive synthesis for short gaps, dependent on a 5 phosphate.
- These findings suggest specific requirements for beta-pol's in vivo function in DNA repair.