Cell death caused by arrested replication of damaged or structurally altered DNA can be avoided in prokaryotic and eukaryotic cells by multiple DNA polymerases that are specialized to bypass DNA damage. Some of these polymerases perform such translesion DNA synthesis of specific types of damage with high genetic fidelity. However, they exhibit greatly reduced fidelity when they operate on undamaged DNA or on DNA with lesions that are (apparently) not cognate substrates. The low fidelity of some of these specialized polymerases when copying undamaged DNA may be physiologically functional, including generating immunoglobulin diversity.
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