Saturation mutagenesis of a CepR binding site as a means to identify new quorum-regulated promoters in Burkholderia cenocepacia.
Burkholderia cenocepacia is an opportunistic pathogen of humans that encodes two genes that resemble the acylhomoserine lactone synthase gene luxI of Vibrio fischeri and three genes that resemble the acylhomoserine lactone receptor gene luxR. Of these, CepI synthesizes octanoylhomoserine lactone (OHL), while CepR is an OHL-dependent transcription factor. In the current study we developed a strategy to identify genes that are directly regulated by CepR. We systematically altered a CepR binding site (cep box) upstream of a target promoter to identify nucleotides that are essential for CepR activity in vivo and for CepR binding in vitro. We constructed 34 self-complementary oligonucleotides containing altered cep boxes, and measured binding affinity for each. These experiments allowed us to identify a consensus CepR binding site. Several hundred similar sequences were identified, some of which were adjacent to probable promoters. Several such promoters were fused to a reporter gene with and without intact cep boxes. This allowed us to identify four new regulated promoters that were induced by OHL, and that required a cep box for induction. CepR-dependent, OHL-dependent expression of all four promoters was reconstituted in Escherichia coli. Purified CepR bound to each of these sites in electrophoretic mobility shift assays.
Departments of Microbiology Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY 14853, USA.
Yuping
Y
Wei
Gina T
GT
Ryan
Ana L
AL
Flores-Mireles
Esther D
ED
Costa
David J
DJ
Schneider
Stephen C
SC
Winans
D001426:Bacterial Proteins / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D057508:Burkholderia cenocepacia / Q000187:drug effects / Q000235:genetics*; D004269:DNA, Bacterial / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D005798:Genes, Bacterial / Q000235:genetics; D006714:Homoserine / Q000031:analogs & derivatives / Q000494:pharmacology; D007783:Lactones / Q000494:pharmacology; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000187:drug effects / Q000235:genetics*; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000187:drug effects; D053038:Quorum Sensing / Q000187:drug effects / Q000235:genetics*; D016415:Sequence Alignment
D001426:Bacterial Proteins; C117246:CepR protein, Burkholderia; D004269:DNA, Bacterial; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D006714:Homoserine
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