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MutS mediates heteroduplex loop formation by a translocation mechanism
D J Allen1, A Makhov, M Grilley
1Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
The EMBO Journal
|July 16, 1997
Summary
Escherichia coli MutS and MutL proteins form DNA loops at mismatches, driven by ATP hydrolysis. This translocation mechanism, enhanced by MutL, may orient DNA repair pathways.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- DNA repair mechanisms are crucial for maintaining genomic stability.
- Escherichia coli MutS and MutL proteins are key components of the methyl-directed mismatch repair pathway.
Purpose of the Study:
- To visualize the interaction of E. coli MutS and MutL with heteroduplex DNA using electron microscopy.
- To elucidate the mechanism of DNA loop formation and translocation mediated by MutS and MutL.
Main Methods:
- Electron microscopy was used to visualize protein-DNA complexes.
- Biochemical assays were performed to study the kinetics of DNA loop formation in the presence of ATP hydrolysis.
Main Results:
- MutS-DNA complexes form protein-stabilized, alpha-shaped loops with mismatches at the apex.
- Loop formation is dependent on ATP hydrolysis, with loop size increasing linearly over time.
- MutL enhances the rate of MutS-mediated DNA loop growth, and both proteins associate with excision intermediates.
Conclusions:
- The observed loop formation suggests an ATP-dependent translocation mechanism for MutS, potentially bidirectional.
- This mechanism may play a role in determining heteroduplex orientation within the methyl-directed repair pathway.