A model for the abrogation of the SOS response by an SOS protein: a negatively charged helix in DinI mimics DNA in its interaction with RecA.

Abstract

DinI is a recently described negative regulator of the SOS response in Escherichia coli. Here we show that it physically interacts with RecA and prevents the binding of single-stranded DNA to RecA, which is required for the activation of the latter. DinI also displaces ssDNA from a stable RecA-DNA cofilament, thus eliminating the SOS signal. In addition, DinI inhibits RecA-mediated homologous DNA pairing, but has no effect on actively proceeding strand exchange. Biochemical data, together with the molecular structure, define the C-terminal alpha-helix in DinI as the active site of the protein. In an unusual example of molecular mimicry, a negatively charged surface on this alpha-helix, by imitating single-stranded DNA, interacts with the loop L2 homologous pairing region of RecA and interferes with the activation of RecA.

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@article{Voloshin2001AMF, title={A model for the abrogation of the SOS response by an SOS protein: a negatively charged helix in DinI mimics DNA in its interaction with RecA.}, author={Oleg N. Voloshin and Benjamin Ramirez and Ad Bax and R. Daniel Camerini-Otero}, journal={Genes & development}, year={2001}, volume={15 4}, pages={415-27} }