Y-family DNA polymerases are a specialized subset of polymerases that facilitate translesion synthesis (TLS), a process that allows the bypass of a variety of DNA lesions. Unlike replicative polymerases, TLS polymerases lack proofreading activity and have low fidelity and low processivity. They use damaged DNA as templates and insert nucleotides opposite the lesions. The active sites of TLS polymerases are large and flexible to allow the accomodation of distorted bases. Expression of Y-family polymerases is often induced by DNA damage and is believed to be highly regulated. TLS is likely induced by the monoubiquitination of the replication clamp PCNA, which provides a scaffold for TLS polymerases to bind in order to access the lesion. Because of their high error rates, TLS polymerases are potential targets for cancer treatment and prevention.