The stacked-X DNA Holliday junction and protein recognition

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• The four-stranded DNA Holliday junction is a key intermediate in DNA recombination and repair.
• Its structure can exist in different conformations, influencing its biological roles.
• Understanding these structures is crucial for comprehending DNA dynamics.

Purpose of the Study:

• To investigate the structural basis of DNA Holliday junctions.
• To explore the sequence-specific stabilization of the stacked-X junction conformation.
• To elucidate the mechanism of structural recognition by junction-resolving enzymes.

Main Methods:

• X-ray crystallography was employed to determine the high-resolution structures.
• Analysis of DNA sequences and their impact on junction stability.
• Comparison of junction structures in the presence and absence of proteins.

Main Results:

• The extended open-X form is observed in protein-bound junctions, while a compact stacked-X structure is seen in free DNA.
• Specific inverted repeat sequences (NCC or ANC motifs) unexpectedly stabilize the stacked-X form.
• The crossover point in stacked-X junctions occurs between the first two nucleotides of the trinucleotide motifs.

Conclusions:

• DNA sequence directly influences Holliday junction structure, favoring the stacked-X conformation.
• This sequence-dependent structural preference may mediate recognition by dimeric junction-resolving enzymes.
• Enzymatic recognition appears to be structure-based rather than sequence-specific.