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Role of HU and DNA supercoiling in transcription repression: specialized nucleoprotein repression complex at gal promoters in Escherichia coli
Author(s) -
Lewis Dale E. A.,
Geanacopoulos Mark,
Adhya Sankar
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.1365-2958.1999.01186.x
Subject(s) - dna supercoil , biology , promoter , psychological repression , microbiology and biotechnology , repressor , lac repressor , dna , transcription (linguistics) , gene , dna replication , transcription factor , genetics , gene expression , linguistics , philosophy
Efficient repression of the two promoters P 1 and P 2 of the gal operon requires the formation of a DNA loop encompassing the promoters. In vitro , DNA looping‐mediated repression involves binding of the Gal repressor (GalR) to two gal operators ( O E and O I ) and binding of the histone‐like protein HU to a specific locus ( hbs ) about the midpoint between O E and O I , and supercoiled DNA. Without DNA looping, GalR binding to O E partially represses P 1 and stimulates P 2. We investigated the requirement for DNA supercoiling and HU in repression of the gal promoters in vivo in strains containing a fusion of a reporter gene, gusA or lacZ , to each promoter individually. While the P 1 promoter was found to be repressible in the absence of DNA supercoiling and HU, the repression of P 2 was entirely dependent upon DNA supercoiling in vivo . The P 2 promoter was fully derepressed when supercoiling was inhibited by the addition of coumermycin in cells. P 2, but not P 1, was also totally derepressed by the absence of HU or the O I operator. From these results, we propose that the repression of the gal promoters in vivo is mediated by the formation of a higher order DNA–multiprotein complex containing GalR, HU and supercoiled DNA. In the absence of this complex, P 1 but not P 2 is still repressed by GalR binding to O E . The specific nucleoprotein complexes involving histone‐like proteins, which repress promoter activity while remaining sensitive to inducing signals, as discussed, may occur more generally in bacterial nucleoids.