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Quorum sensing in Vibrio fischeri : elements of the luxI promoter
Author(s) -
Egland Kristi A.,
Greenberg E. P.
Publication year - 1999
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1999.01261.x
Subject(s) - operon , biology , random hexamer , autoinducer , quorum sensing , promoter , vibrio , gene , bioreporter , start codon , escherichia coli , direct repeat , repressor lexa , transcription (linguistics) , genetics , microbiology and biotechnology , repressor , transcription factor , reporter gene , gene expression , bacteria , messenger rna , linguistics , philosophy , virulence , base sequence
Although cell density‐dependent regulation of the luminescence genes in Vibrio fischeri is a model for quorum sensing in Gram‐negative bacteria, relatively little is known about the promoter of the luminescence operon. The luminescence operon is activated by the LuxR protein, which requires a diffusible acylhomoserine lactone signal. The lux box, a 20 bp inverted repeat, is located in the luxI promoter region and is required for LuxR‐dependent induction of the luminescence genes. Using primer extension, we mapped the LuxR‐dependent transcriptional start site of the lux operon to 19 bp upstream of the luxI start codon. This indicates that the lux box is centred at −42.5 bp from the start of transcription. To gain evidence about the location of the −10 sequence, we placed a consensus −35 hexamer at different locations relative to the luxI transcriptional start site and measured constitutive levels of luminescence in recombinant Escherichia coli . The strongest constitutive promoter contained a TATAGT hexamer 17 bp from the −35 consensus sequence and 6 bp from the transcriptional start site. We propose that this is the −10 hexamer. Also in recombinant E. coli , both half‐sites of the lux box were required for LuxR‐dependent gene activation and for activation by an autoinducer‐independent, monomeric LuxR deletion protein. LuxR‐dependent activation of luminescence was eliminated when the lux box was centred at −47.5, −52.5 and −62.5 with respect to the luxI transcriptional start site. Our evidence, taken together with other information, points to a model in which a LuxR dimer overlaps the −35 region of the luxI promoter and functions as an ambidextrous activator with each LuxR subunit interacting with a different region of RNA polymerase.