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.
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.
Genetics and Biochemistry Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
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ON
Voloshin
B E
BE
Ramirez
A
A
Bax
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RD
Camerini-Otero
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001483:Base Sequence; D017931:DNA Primers; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D029968:Escherichia coli Proteins; D018716:Molecular Mimicry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011938:Rec A Recombinases / Q000378:metabolism*; D013014:SOS Response, Genetics
D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; C422844:DinI protein, E coli; D029968:Escherichia coli Proteins; D011938:Rec A Recombinases