Mismatch repair deals with correcting mismatches of the normal bases, that fails to maintain normal base pairing (A•T, C•G)
It can enlist the aid of enzymes involved in both base-excision repair (BER) and nucleotide-excision repair (NER) as well as using enzymes specialized for this function.
- Recognition of a mismatch requires several different proteins
- Cutting the mismatch out also requires several proteins
Repairing Strand Breaks
Ionizing radiation and certain chemicals can produce both single-strand breaks (SSBs) and double-strand breaks (DSBs) in the DNA backbone.
- Single-Strand Breaks (SSBs)
Breaks in a single strand of the DNA molecule are repaired using the same enzyme systems that are used in Base-Excision Repair (BER).
- Double-Strand Breaks (DSBs)
There are two mechanisms by which the cell attempts to repair a complete break in a DNA molecule.
- Direct joining of the broken ends. This requires proteins that recognize and bind to the exposed ends and bring them together for ligating. They would prefer to see some complementary nucleotides but can proceed without them so this type of joining is also called Nonhomologous End-Joining (NHEJ).
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