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Negative transcriptional regulation of a positive regulator: the expression of malT , encoding the transcriptional activator of the maltose regulon of Escherichia coli , is negatively controlled by Mlc
Author(s) -
Decker Katja,
Plumbridge Jacqueline,
Boos Winfried
Publication year - 1998
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.1365-2958.1998.00694.x
Subject(s) - regulon , biology , operon , repressor , gene , transcriptional regulation , activator (genetics) , lac operon , regulation of gene expression , escherichia coli , genetics , regulator gene , regulator , microbiology and biotechnology , gene expression
The maltose regulon consists of 10 genes encoding a multicomponent and binding protein‐dependent ABC transporter for maltose and maltodextrins as well as enzymes necessary for the degradation of these sugars. MalT, the transcriptional activator of the system, is necessary for the transcription of all mal genes. MalK, the energy‐transducing subunit of the transport system, acts phenotypically as repressor, particularly when overproduced. We isolated an insertion mutation that strongly reduced the repressing effect of overproduced MalK. The affected gene was sequenced and identified as mlc , a known gene encoding a protein of unknown function with homology to the Escherichia coli NagC protein. The loss of Mlc function led to a threefold increase in malT expression, and the presence of mlc on a multicopy plasmid reduced malT expression. By DNaseI protection assay, we found that Mlc protected a DNA region comprising positions + 1 to + 23 of the malT transcriptional start point. Using a mlc – lacZ fusion in a mlc and mlc + background, we found that Mlc represses its own expression. As Mlc also regulates another operon ( manXYZ , see pages 369–379 of this issue), it may very well constitute a new global regulator of carbohydrate utilization.