DNA double-strand break processing involved in repair via single-strand annealing

Definition

Target type: biologicalprocess

The 5' to 3' exonucleolytic resection of the DNA at the site of the break to form a 3' single-strand DNA overhang that results in the repair of a double strand break via single-strand annealing. [GOC:dph, GOC:tb]

DNA double-strand breaks (DSBs) are highly deleterious lesions that can lead to genomic instability and cell death if not repaired efficiently. Single-strand annealing (SSA) is a homologous recombination (HR) pathway that repairs DSBs by using homologous sequences located on the same or sister chromatid. SSA is a relatively simple pathway compared to other HR pathways, involving only a few key steps.

1. **Resection**: Following DSB formation, 5' to 3' exonucleases, such as EXO1 and BLM, resect the 5' ends of the broken DNA strands, generating 3' single-stranded tails.

2. **Annealing**: The 3' single-stranded tails from both ends of the DSB invade the homologous sequence on the other broken DNA strand, forming a "D-loop" structure. This process is facilitated by the RAD52 protein, which promotes annealing of the complementary single-stranded tails.

3. **Ligation**: The annealed DNA strands are ligated together by DNA ligases, such as LIG1, to form a single continuous DNA molecule.

4. **Gap Repair**: The gaps in the newly synthesized DNA are filled in by DNA polymerase, using the other strand as a template.

5. **Deletion**: SSA repair typically results in the deletion of the DNA sequence between the two homologous regions that were used for annealing. This is because the sequences between the break points are not replicated during the repair process.

SSA repair is particularly important for repairing DSBs that occur within repetitive sequences, such as microsatellites. These sequences are prone to deletions and insertions, which can lead to genomic instability. SSA can repair these DSBs without the need for extensive homology searching, which is required for other HR pathways. However, SSA repair is also prone to errors, as the deletion of sequences can disrupt gene function.

In summary, SSA repair is a specialized HR pathway that repairs DSBs by using homologous sequences located on the same or sister chromatid. This process involves resection of the broken DNA ends, annealing of the single-stranded tails, ligation of the annealed strands, gap repair, and deletion of the sequence between the homologous regions. SSA is particularly important for repairing DSBs within repetitive sequences, but it is also prone to errors, as the deletion of sequences can disrupt gene function.'
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Proteins (1)

Compounds (17)