Strand asymmetry influences mismatch resolution during a single-strand annealing

Area of Science:

• Molecular Biology
• Genomics
• Evolutionary Biology

Background:

• DNA repair mechanisms are crucial for maintaining genome integrity.
• Understanding the molecular basis of DNA repair biases is essential for explaining genome evolution.
• Existing methods struggle to differentiate DNA repair contributions from DNA damage effects.

Purpose of the Study:

• To develop a novel genome-wide assay to study DNA repair biases.
• To investigate the influence of genomic context on DNA mismatch repair.
• To elucidate the mechanisms underlying DNA repair biases.

Main Methods:

• Development of a genome-wide assay using barcoded transposons in mouse embryonic stem cells.
• Induction of double-strand breaks within tandem repeats to generate mismatches.
• Analysis of mismatch resolution bias based on 3' flap length during single-strand annealing.

Main Results:

• A significant bias (60-80%) in mismatch resolution favoring the strand with the longest 3' flap was observed.
• The genomic location of the lesion and mismatch type had minimal impact on this bias.
• Reversal of the bias was achieved by altering the double-strand break position, thereby changing the 3' flap orientation.

Conclusions:

• The processing of double-strand breaks is a primary determinant of mismatch repair bias during single-strand annealing.
• This finding provides critical insights into the molecular mechanisms shaping genome nucleotide landscapes.
• The developed assay offers a powerful tool for dissecting DNA repair processes.