Homologous Recombination

Homologous Recombination is a high-fidelity DNA repair pathway that uses a homologous sequence as a template to accurately restore genetic information at double-strand break sites ¹.

How It Works

Homologous recombination (HR) begins when a double-strand break (DSB) is detected and the broken ends are resected by nucleases to generate 3’ single-stranded DNA overhangs. The recombinase RAD51 coats these overhangs, forming a nucleoprotein filament that searches for homologous sequences on a sister chromatid or exogenous donor template.

Once a homologous sequence is found, the filament invades the template strand, forming a displacement loop (D-loop). DNA polymerase extends the invading strand using the template, and the resulting structure is resolved through Holliday junction intermediates or synthesis-dependent strand annealing.

In genome engineering, HR is exploited by providing exogenous donor templates with homology arms flanking the desired edit. This enables precise insertions, replacements, or corrections at targeted loci. However, HR is primarily active during the S and G2 phases of the cell cycle, limiting its efficiency in non-dividing cells ¹.

Computational Considerations

Computational tools model HR efficiency by analyzing homology arm length, GC content, secondary structure propensity, and chromatin accessibility at the target locus. Machine learning models trained on experimental HR outcomes help predict optimal donor template configurations, reducing the experimental iteration required for successful knock-in experiments ².

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