Escherichia coli’s DNA polymerase IV (Pol IV/DinB), a member of the Y family of error-prone polymerases, is induced during
the SOS response to DNA damage and is responsible for translesion bypass and adaptive (stress-induced) mutation. In this
study, the localization of Pol IV after DNA damage was followed using fluorescent fusions. After exposure of E. coli to DNAdamaging
agents, fluorescently tagged Pol IV localized to the nucleoid as foci. Stepwise photobleaching indicated60% of the
foci consisted of three Pol IV molecules, while40% consisted of six Pol IV molecules. Fluorescently tagged Rep, a replication
accessory DNA helicase, was recruited to the Pol IV foci after DNA damage, suggesting that the in vitro interaction between Rep
and Pol IV reported previously also occurs in vivo. Fluorescently tagged RecA also formed foci after DNA damage, and Pol IV
localized to them. To investigate if Pol IV localizes to double-strand breaks (DSBs), an I-SceI endonuclease-mediated DSB was
introduced close to a fluorescently labeled LacO array on the chromosome. After DSB induction, Pol IV localized to the DSB site
in70% of SOS-induced cells. RecA also formed foci at the DSB sites, and Pol IV localized to the RecA foci. These results suggest
that Pol IV interacts with RecA in vivo and is recruited to sites of DSBs to aid in the restoration of DNA replication.
Escherichia coli’s DNA polymerase IV (Pol IV/DinB), a member of the Y family of error-prone polymerases, is induced duringthe SOS response to DNA damage and is responsible for translesion bypass and adaptive (stress-induced) mutation. In thisstudy, the localization of Pol IV after DNA damage was followed using fluorescent fusions. After exposure of E. coli to DNAdamagingagents, fluorescently tagged Pol IV localized to the nucleoid as foci. Stepwise photobleaching indicated60% of thefoci consisted of three Pol IV molecules, while40% consisted of six Pol IV molecules. Fluorescently tagged Rep, a replicationaccessory DNA helicase, was recruited to the Pol IV foci after DNA damage, suggesting that the in vitro interaction between Repand Pol IV reported previously also occurs in vivo. Fluorescently tagged RecA also formed foci after DNA damage, and Pol IVlocalized to them. To investigate if Pol IV localizes to double-strand breaks (DSBs), an I-SceI endonuclease-mediated DSB wasintroduced close to a fluorescently labeled LacO array on the chromosome. After DSB induction, Pol IV localized to the DSB sitein70% of SOS-induced cells. RecA also formed foci at the DSB sites, and Pol IV localized to the RecA foci. These results suggestthat Pol IV interacts with RecA in vivo and is recruited to sites of DSBs to aid in the restoration of DNA replication.
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