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Topoisomerase function during replication-independent chromatin assembly in yeast
1Department of Biochemistry, University of Alberta, Edmonton, Canada.
Molecular and Cellular Biology
|July 1, 1997
Summary
Both DNA topoisomerase I and II enzymes are crucial for efficient chromatin assembly in yeast. This study reveals that both enzymes can independently provide the necessary DNA relaxation activity for this process.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- DNA topoisomerases I and II are key nuclear enzymes that manage DNA torsional strain.
- Topoisomerase I is considered dominant in chromatin assembly during early development.
Purpose of the Study:
- To investigate the differential roles of topoisomerases I and II in chromatin assembly in Saccharomyces cerevisiae.
- To determine if both enzymes are essential or if they can be functionally redundant.
Main Methods:
- Utilized a combined biochemical and pharmacological approach in yeast mutants.
- Assessed plasmid supercoiling and nucleosome deposition as measures of chromatin assembly efficiency.
- Employed a topoisomerase II inhibitor (VP-16) to assess enzyme activity.
Main Results:
- Chromatin assembly was significantly impaired in yeast lacking topoisomerase I and having a temperature-sensitive topoisomerase II.
- Restoring either topoisomerase I or II activity fully rescued the impaired chromatin assembly.
- Topoisomerase II activity during assembly was unaffected by the presence or absence of topoisomerase I.
Conclusions:
- Both DNA topoisomerase I and II can independently provide the DNA relaxation activity required for efficient chromatin assembly in yeast.
- The enzymes exhibit functional redundancy in supporting chromatin assembly in mitotically cycling yeast cells.