Double locking of an Escherichia coli promoter by two repressors prevents premature colicin expression and cell lysis.
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.
Department of Biology, University of Ljubljana, 1000 Ljubljana, Slovenia. matej.butala@bf.uni-lj.si
Matej
M
Butala
Silva
S
Sonjak
Simona
S
Kamenšek
Milan
M
Hodošček
Douglas F
DF
Browning
Darja
D
Žgur-Bertok
Stephen J W
SJ
Busby
D001426:Bacterial Proteins / Q000378:metabolism*; D001433:Bacteriolysis; D001483:Base Sequence; D003087:Colicins / Q000096:biosynthesis*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D029968:Escherichia coli Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D008954:Models, Biological; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012697:Serine Endopeptidases / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D000099160:LexA Repressor Protein
D001426:Bacterial Proteins; D003087:Colicins; D029968:Escherichia coli Proteins; D012697:Serine Endopeptidases; D014157:Transcription Factors; D000099160:LexA Repressor Protein; C499695:IscR protein, E coli