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TLS
in Escherichia coli strain K-12 substr. MG1655
translesion synthesis
(also known as DNA damage tolerance)
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Escherichia coli possesses five known DNA polymerases (pols). Pol III holoenzyme is the cell's main replicase, while Pol I is responsible for the maturation of Okazaki fragments and filling gaps generated during nucleotide excision repair.
Pols II, IV and V are significantly upregulated as part of the cell's global SOS response to DNA damage and under these conditions, may alter the fidelity of DNA replication by potentially interfering with the ability of Pols I and III to complete their cellular functions.
In Escherichia coli, cell survival and genomic stability after UV radiation depends on repair mechanisms induced as part of the SOS response to DNA damage. The early phase of the SOS response is mostly dominated by accurate DNA repair, while the later phase is characterized with elevated mutation levels caused by error-prone DNA replication. SOS mutagenesis is largely the result of the action of DNA polymerase V (Pol V), which has the ability to insert nucleotides opposite various DNA lesions in a process termed translesion DNA synthesis (TLS). Pol V is a low-fidelity polymerase that is composed of UmuD'(2)C and is encoded by the umuDC operon. Pol V is strictly regulated in the cell so as to avoid genomic mutation overload. RecA nucleoprotein filaments (RecA*), formed by RecA binding to single-stranded DNA with ATP, are essential for pol V-catalyzed TLS both in vivo and in vitro.
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