Related Experiment Videos
Top3 processes recombination intermediates and modulates checkpoint activity after DNA damage.
Hocine W Mankouri1, Ian D Hickson
1Cancer Research UK Laboratories, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
Molecular Biology of the Cell
|August 11, 2006
Summary
The catalytic activity of Top3 is crucial for normal S-phase progression after DNA damage, not for checkpoint activation. Top3 processes recombination intermediates and modulates checkpoint activity during S phase.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- Top3 is essential for DNA replication and repair in Saccharomyces cerevisiae.
- TOP3 mutations lead to genomic instability, including hyperrecombination and checkpoint defects.
- The catalytic activity of Top3, specifically its decatenation function, is critical for resolving DNA topological problems.
Purpose of the Study:
- To investigate the role of Top3's catalytic activity in DNA damage response during S phase.
- To determine if Top3's decatenation function is required for DNA damage checkpoint activation.
- To elucidate the downstream pathways affected by impaired Top3 function after DNA damage.
Main Methods:
- Overexpression of a dominant-negative TOP3 allele (TOP3(Y356F)) lacking catalytic activity.
- Exposure of yeast cells to methyl methanesulfonate (MMS) to induce DNA damage.
- Analysis of S-phase progression, cell cycle delays, and DNA structure persistence using microscopy and cell cycle analysis.
- Investigating the role of Rad51 function in the observed phenotypes.
Main Results:
- Overexpression of TOP3(Y356F) impaired S-phase progression and led to persistent abnormal DNA structures (X-shaped molecules) after MMS treatment.
- The impaired S-phase progression was attributed to a persistent checkpoint-mediated cell cycle delay, which could be bypassed by caffeine.
- Top3's catalytic activity is not required for DNA damage checkpoint activation but is essential for normal S-phase progression post-damage.
- The observed phenotypes were downstream of Rad51 function.
Conclusions:
- Top3's catalytic activity is essential for resolving DNA structures that impede S-phase progression following DNA damage.
- Top3 plays a dual role in S phase: processing homologous recombination intermediates and modulating DNA damage checkpoint activity.
- These findings highlight the importance of Top3 in maintaining genomic integrity during DNA replication and repair.