Probing specific sequences on single DNA molecules with bioconjugated fluorescent nanoparticles

Area of Science:

• Biophysics
• Molecular Biology
• Nanotechnology

Background:

• Traditional organic fluorophores for DNA imaging suffer from photobleaching and blinking.
• Nanoparticle probes offer enhanced brightness and photostability compared to single organic fluorophores.

Purpose of the Study:

• To develop and characterize fluorescent nanoparticle-DNA-binding protein conjugates for high-resolution DNA analysis.
• To assess the DNA binding and enzymatic activity of nanoparticle-conjugated restriction enzymes.

Main Methods:

• Covalent conjugation of 20-nm fluorescent nanoparticles to the EcoRI restriction enzyme.
• Immobilization and stretching of single DNA molecules on a solid surface.
• Multicolor fluorescence microscopy for visualizing nanoparticle-DNA interactions.

Main Results:

• EcoRI-nanoparticle conjugates exhibit specific DNA binding and cleavage activity, similar to the native enzyme.
• Conjugates bind to specific DNA sequences even without magnesium ions, but do not cleave DNA.
• Nanoparticle binding sites on stretched single DNA molecules were directly visualized.

Conclusions:

• Fluorescent nanoparticle-protein conjugates provide a superior alternative to organic fluorophores for DNA imaging.
• This technique allows for direct optical observation of DNA-protein interactions on single DNA molecules.
• The method opens new avenues for optical gene mapping and studying DNA-protein dynamics.