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.
Voloshin
O N
ON
Genetics and Biochemistry Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
Ramirez
B E
BE
Bax
A
A
Camerini-Otero
R D
RD
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