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Autoregulated expression of the gene coding for the leucine-responsive protein, Lrp, a global regulator in Salmonella enterica serovar Typhimurium

Department of Microbiology, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Ireland

Correspondence
Charles J. Dorman
cjdorman{at}tcd.ie

In this study, the lrp gene encoding the leucine-responsive regulatory protein (Lrp) in Salmonella enterica serovar Typhimurium was found to be negatively autoregulated. Its transcription start site was determined by primer extension analysis, showing that the lrp promoter is located at a different site to that inferred previously from the S. Typhimurium genome sequence. Chromosomal DNA fragments that include the promoter region were bound by purified Lrp protein in vitro, producing up to four distinct protein–DNA complexes. DNase I footprinting identified regions that were protected by the protein in vitro as well as bases that became hypersensitive to DNase I treatment following Lrp binding. A clear pattern of periodic hypersensitivity was detected between positions –130 and +15 that was consistent with wrapping of the DNA around Lrp in a nucleoprotein complex that includes the putative promoter region. Lrp–DNA interaction in this region was fully consistent with the observed repression of lrp transcription by this protein. Leucine was found to modulate Lrp-mediated autorepression by remodelling the Lrp–DNA nucleoprotein complex.

Present address: Division of Infectious Diseases, Children's Hospital, Enders Building, Harvard University, 300 Longwood Avenue, Boston, MA 02115, USA.