HMG box proteins interact with multiple tandemly repeated (GCC)n (GGC)m DNA sequences

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Tandemly repeated DNA sequences can form non-standard base-paired hairpin structures.
• Triplet repeat expansion in genomic DNA is linked to neurological disorders and cancer.

Purpose of the Study:

• To investigate the formation and characteristics of DNA complexes from annealing (GCC)15 and (GCC)10 strands.
• To determine the interaction of HMG box proteins with these DNA structures.

Main Methods:

• Annealing of synthetic DNA strands ((GCC)15 and (GCC)10).
• Native gel electrophoresis to detect and characterize DNA complexes.
• Exonuclease VII (Exo VII) digestion to differentiate duplexes with single-stranded tails from branched structures.
• Electrophoretic mobility shift assays (EMSAs) with HMG box proteins (HMGb).

Main Results:

• Annealing (GCC)15 with (GCC)10 yielded up to five complexes, including duplexes with single-stranded tails and branched structures.
• Branched DNA structures were resistant to Exo VII digestion and exhibited low mobility on native gels.
• HMG box proteins (HMGb) showed strong binding to branched DNA structures compared to normal duplexes.

Conclusions:

• Branched DNA structures, potentially arising during replication of triplet repeats, can bind abundant nuclear proteins like HMG box proteins.
• The interaction of HMG box proteins and histone H1 with these branched intermediates may influence triplet repeat expansion, contributing to disease pathogenesis.