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Osmoregulation in Lactococcus lactis : BusR, a transcriptional repressor of the glycine betaine uptake system BusA
Author(s) -
Romeo Yves,
Obis David,
Bouvier Jean,
Guillot Alain,
Fourçans Aude,
Bouvier Isabelle,
Gutierrez Claude,
Mistou MichelYves
Publication year - 2003
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.1365-2958.2003.03362.x
Subject(s) - biology , lactococcus lactis , operon , transcription (linguistics) , microbiology and biotechnology , repressor , gene , genetics , plasmid , promoter , gene expression , escherichia coli , bacteria , lactic acid , linguistics , philosophy
Summary The busA ( opuA ) locus of Lactococcus lactis encodes a glycine betaine uptake system. Transcription of busA is osmotically inducible and its induction after an osmotic stress is reduced in the presence of glycine betaine. Using a genetic screen in CLG802, an Escherichia coli strain carrying a lacZ transcriptional fusion expressed under the control of the busA promoter, we isolated a genomic fragment from the L. lactis subsp. cremoris strain MG1363, which represses transcription from busA p . The cloned locus responsible for this repression was identified as a gene present upstream from the busA operon, encoding a putative DNA binding protein. This gene was named busR . Electrophoretic mobility shift and footprinting experiments showed that BusR is able to bind a site that overlaps the busA promoter. Overexpression of busR in L. lactis reduced expression of busA . Its disruption led to increased and essentially constitutive transcription of busA at low osmolarity. Therefore, BusR is a major actor of the osmotic regulation of busA in L. lactis .