We show that self cleavage of LexA repressor is prevented by binding to specific DNA operator targets, depends on LexA dissociation from the targets and, hence, this controls the SOS response. Distance measurements using EPR spectroscopy reveal that in unbound LexA the DNA binding domains sample different conformations, one of which is captured when bound to operator targets, precluding RecA interaction. Modulation of LexA activity changes the occurrence of persister cells in bacterial populations.
COBISS.SI-ID: 2368847
The chapter named The LexA regulatory system for the second edition of "Encyclopedia of Biological Chemistry" published by Elsevier. An invitation from Nancy L. Craig (Howard Hughes Medical Institute).
The synthesis of Eschericha coli colicins is lethal to the producing cell and is repressed during normal growth by the LexA transcription factor, which is the master repressor of the SOS system for repair of DNA damage. Following DNA damage, LexA is inactivated and SOS repair genes are induced immediately, but colicin production is delayed and induced only in terminally damaged cells. The cause of this delay is unknown. Here we identify the global transcription repressor, IscR, as being directly responsible for the delay in colicin K expression during the SOS response and identify the DNA target for IscR at the colicin K operon promoter. Hence, this promoter is 'double locked' to ensure that suicidal colicin K production is switched on only as a last resort.