Efficient modification of λ-DNA substrates for single-molecule studies

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Site-specific modification of long DNA substrates is crucial for studying protein-nucleic acid interactions.
• Current methods for modifying long DNA, like bacteriophage lambda (λ)-DNA, often involve complex multi-step ligations with low efficiency.
• Developing efficient tools for precise DNA modification is essential for advancing molecular biology research.

Purpose of the Study:

• To create a molecular toolkit for the rapid and efficient preparation of modified λ-DNA.
• To enable the introduction of specific sequences, tertiary structures, and chemical modifications at user-defined sites within λ-DNA.
• To demonstrate the utility of the toolkit in studying protein-DNA interactions, specifically the role of Saccharomyces cerevisiae Proliferating Cell Nuclear Antigen (yPCNA) in DNA repair and disease-related mechanisms.

Main Methods:

• Utilized a set of PCR cassettes for high-yield (90-100%) introduction of recombinant DNA sequences into the λ-phage genome.
• Employed an improved nicking enzyme-based strategy for site-specific insertion of extrahelical structures and chemical modifications.
• Investigated the interactions of yPCNA with modified λ-DNA substrates, including 5'-ssDNA flaps, (CAG)13 triplet repeats, and homoduplex DNA, using Saccharomyces cerevisiae Replication Factor C (yRFC) for loading.

Main Results:

• The molecular toolkit allows for rapid and efficient preparation of modified λ-DNA with high fidelity.
• Demonstrated successful loading of yPCNA onto various DNA structures, including ssDNA flaps and triplet repeats, mediated by yRFC.
• Observed that yPCNA becomes trapped on (CAG)13 triplet repeat structures, providing evidence for a proposed mechanism of triplet repeat expansion.

Conclusions:

• The developed molecular toolkit significantly simplifies the site-specific modification of long DNA substrates like λ-DNA.
• This toolkit facilitates detailed investigations into protein-DNA interactions and the mechanisms underlying DNA-related diseases, such as triplet repeat expansion.
• The methodology is expected to be broadly applicable to diverse research areas requiring precisely engineered long DNA molecules.