DNA base identification by electron microscopy.

Area of Science:

• Genomics
• Molecular Biology
• Microscopy

Background:

• Current DNA sequencing methods using fluorescent microscopy are limited to short DNA molecules.
• Accurate sequencing of long, intact DNA molecules (>10,000 base-pairs) is crucial for genomic research advancements.

Purpose of the Study:

• To develop a method for direct visualization and sequencing of long, intact DNA molecules using electron microscopy.
• To demonstrate the identification of individual DNA base pairs within intact DNA molecules.

Main Methods:

• Enzymatic incorporation of modified nucleotides (dUTP) with heavy atoms (mercury) into DNA.
• Utilizing annular dark-field scanning transmission electron microscopy (ADF-STEM) for enhanced image contrast.
• Sequencing a synthetic DNA molecule (3,272 base-pairs) and a viral genome (7,249 base-pairs).

Main Results:

• First identification of DNA base pairs within intact DNA molecules using electron microscopy.
• Successful visualization and identification of individually labeled bases in synthetic and viral DNA.
• Demonstrated proof of principle for heavy-atom labeling at A-T positions.

Conclusions:

• Electron microscopy, combined with heavy-atom labeling, offers a novel approach for sequencing long DNA molecules.
• This technique has the potential to significantly accelerate complex genomic discoveries.
• Further refinements could enable full sequencing of long DNA and identification of all base types.