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DNA strand break-mediated partitioning of poly(ADP-ribose) polymerase function
1Institute of Pharmacology and Toxicology, University of Zürich-Tierspital, Switzerland.
Biochemistry
|August 16, 1994
Summary
The nuclear enzyme poly(ADP-ribose) polymerase (PARP) requires a specific ratio of two molecules per DNA break for optimal activity in DNA repair. This finding challenges the strict automodification mechanism, suggesting a partitioning model for PARP activation.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Poly(ADP-ribose) polymerase (PARP) is a crucial nuclear enzyme involved in DNA excision repair.
- PARP binds to DNA strand breaks via its Zn(2+)-finger domain, initiating ADP-ribose polymer formation.
Purpose of the Study:
- To investigate the mechanism of poly(ADP-ribose) formation during DNA repair.
- To determine the optimal stoichiometry of PARP for its automodification reaction.
Main Methods:
- Enzyme activity assays using various linearized and nicked circular DNA fragments.
- Quantitative analysis of polymer formation at different PARP-to-DNA ratios.
Main Results:
- Optimal PARP activity and maximal polymer formation occurred at a strict 2:1 stoichiometry (PARP molecules to DNA fragment).
- Deviations from this ratio significantly decreased polymer formation.
- The number of DNA strand breaks, not just the presence of DNA, dictated the stoichiometric dependence.
Conclusions:
- The poly(ADP-ribosyl)ation mechanism is not a strict automodification process.
- PARP likely partitions into catalytically active (DNA-bound) and inactive (polymer acceptor) populations mediated by DNA strand breaks.