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Updated: Jun 18, 2026
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Single-Molecule Real-Time Visualization of DNA Unwinding by CMG Helicase
Published on: September 27, 2024
Does BLM helicase unwind nucleosomal DNA?
Satoru Fujimoto1, Miroslav Tomschik, Jordanka Zlatanova
1Department of Molecular Biology, College of Agriculture, University of Wyoming, 1000 East University Ave., Laramie, WY 82071, USA.
Biochemistry and Cell Biology = Biochimie Et Biologie Cellulaire
|November 26, 2009
Summary
Bloom
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- RecQ helicases are vital for maintaining genomic stability by resolving complex DNA structures.
- Bloom syndrome protein (BLM) is a RecQ helicase with DNA unwinding and strand annealing activities.
- Understanding BLM's function on chromatin is crucial for comprehending its role in DNA repair and disease.
Purpose of the Study:
- To investigate the DNA unwinding activity of BLM on nucleosomal DNA, a natural substrate.
- To determine the influence of the single-stranded DNA-binding protein RPA on BLM's activity on forked DNA and nucleosomal DNA.
- To elucidate the requirements for BLM to unwind compacted DNA structures.
Main Methods:
- Biochemical assays were used to assess DNA unwinding activity.
- A DNA template with a nucleosome-positioning sequence and forked DNA was synthesized.
- Reconstitution of histone octamers onto DNA to form forked mononucleosomes was performed.
- The effect of RPA on BLM activity was evaluated on both naked and nucleosomal DNA substrates.
Main Results:
- Full-length BLM showed no detectable unwinding activity on forked DNA, while truncated BLM did.
- RPA enhanced the unwinding activity of both BLM forms on forked DNA.
- Full-length BLM failed to unwind forked nucleosomal DNA, whereas truncated BLM showed partial unwinding.
- RPA did not significantly enhance BLM's unwinding activity on nucleosomal DNA.
Conclusions:
- Full-length BLM requires additional factors beyond RPA to unwind nucleosomal DNA in vivo.
- The strand-annealing activity of BLM may play a role in its interaction with nucleosomal DNA.
- BLM's unwinding of compacted DNA structures is complex and may involve multiple protein interactions.
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