Structure-specific endonucleolytic cleavage of nucleic acids by eubacterial DNA polymerases

Area of Science:

• Molecular Biology
• Enzymology
• Nucleic Acid Chemistry

Background:

• Previously identified 5' exonucleases in eubacterial DNA polymerases.
• These enzymes were thought to function primarily in DNA repair or processing.

Purpose of the Study:

• To characterize the substrate specificity and mechanism of action of these 5' exonucleases.
• To determine if these enzymes exhibit endonuclease activity and under what conditions.

Main Methods:

• Enzyme assays using various DNA and RNA substrates with defined structures.
• Kinetic analysis of cleavage reactions.
• Investigating the role of primers and hybridization in enzyme activity.

Main Results:

• Demonstrated that 5' exonucleases are structure-specific endonucleases cleaving single-stranded DNA/RNA at duplex bifurcations.
• Cleavage is not coupled to DNA synthesis but is significantly accelerated by primers.
• Enzymes access cleavage sites by moving along the nucleic acid strand.
• Up to 200-nucleotide single-stranded arms can be cleaved.
• Targeted cleavage of any linear single-stranded nucleic acid is achievable through hybridization with a complementary oligonucleotide.

Conclusions:

• The 5' exonucleases of eubacterial DNA polymerases possess novel endonuclease activity.
• This activity can be harnessed for targeted nucleic acid cleavage by designing specific hybridization probes.
• Offers a new tool for molecular biology applications requiring precise nucleic acid degradation.