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DNA trajectory in the Gal repressosome
Szabolcs Semsey1, Michail Y Tolstorukov, Konstantin Virnik
1Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Genes & Development
|August 4, 2004
Summary
The Gal repressosome complex in E. coli uses an antiparallel DNA loop orientation for optimal repression. This finding clarifies the structure of this crucial transcription regulatory machine.
Area of Science:
- Molecular Biology
- Genetics
- Structural Biology
Background:
- The Gal repressosome is a complex that regulates gal operon transcription in E. coli.
- It involves GalR dimers binding to operators OE and OI, forming a DNA loop.
- HU protein stabilizes the complex, and GalR tetramerization is key.
Purpose of the Study:
- To determine the DNA loop trajectory within the Gal repressosome.
- To investigate the parallel (PL) versus antiparallel (AL) operator alignment.
- To understand the structural basis of transcriptional repression.
Main Methods:
- Structure-based genetic analysis of GalR mutants.
- In vitro transcription repression assays.
- Construction of hybrid operators and mutant GalR heterodimers to isolate specific DNA trajectories.
Main Results:
- Four potential DNA trajectories were identified based on operator alignment and GalR dimer stacking.
- Mutant analysis revealed that OE and OI operators adopt an antiparallel orientation.
- This antiparallel arrangement occurs within an under-twisted DNA loop, with HU binding at the loop apex.
Conclusions:
- The Gal repressosome utilizes an antiparallel DNA loop orientation for efficient transcriptional repression.
- This structure is energetically optimal and positions the HU-binding site critically.
- The methodology can be applied to study other complex nucleoprotein machines.