A four-way junction with triple-helical arms: design, characterization, and stability

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• DNA junctions are critical structural motifs involved in various biological processes.
• Understanding the stability and formation of complex DNA structures is essential for molecular biology applications.

Purpose of the Study:

• To demonstrate the formation and characterize the structure of a four-way DNA junction with four triple-helical arms (J(T1T3)).
• To investigate the contribution of individual arms to the overall stability of the junction.
• To elucidate the role of sodium ions in the folding and stabilization of these DNA junctions.

Main Methods:

• Chemical methods: Polyacrylamide gel electrophoresis and chemical footprinting using Osmium tetroxide (OsO4).
• Physical methods: UV absorbance melting and Differential Scanning Calorimetry (DSC).
• Structural analysis by comparing the full junction (J(T1T3)) with simplified substructures (J(T1) and J(T3)).

Main Results:

• Successful assembly of the J(T1T3) four-way junction from synthetic DNA strands.
• Polyacrylamide gel electrophoresis confirmed the presence of a single, stable species.
• OsO4 footprinting indicated no thymine cleavage at the branch point, supporting the proposed structure.
• Thermal stability studies showed triple-helical arms are more stable than double-helical arms.
• J(T1T3) was found to be slightly more stable than its substructures, with comparable calorimetric transition enthalpies.
• Sodium ions significantly enhanced junction stability and promoted folding into stacked X-structures.

Conclusions:

• The study successfully demonstrated the formation of a stable four-way DNA junction with four triple-helical arms.
• The stability of the junction is influenced by the triple-helical arms and significantly enhanced by sodium ions.
• Junction formation is robust and not overly sensitive to pH, ionic strength, sequence, or loop position.