Double locking of an Escherichia coli promoter by two repressors prevents premature colicin expression and cell lysis

Research output: Contribution to journalArticlepeer-review


  • Silva Sonjak
  • Simona Kamenšek
  • Milan Hodošček
  • Darja Žgur-Bertok

Colleges, School and Institutes


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. Our results suggest that, IscR stabilizes LexA at the cka promoter after DNA damage thus, preventing its cleavage and inactivation, and this cooperation ensures that suicidal colicin K production is switched on only as a last resort. A similar mechanism operates at the regulatory region of other colicins and, hence, we suggest that many promoters that control the expression of 'lethal' genes are double locked.


Original languageEnglish
Pages (from-to)129-39
Number of pages11
JournalMolecular Microbiology
Issue number1
Publication statusPublished - 2012