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Post‐transcriptional enhancement of Escherichia coli bgl operon silencing by limitation of BglG‐mediated antitermination at low transcription rates
Author(s) -
Dole Sudhanshu,
Kühn Sandra,
Schnetz Karin
Publication year - 2002
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.1365-2958.2002.02734.x
Subject(s) - antitermination , operon , biology , transcription (linguistics) , rpos , trp operon , genetics , lac operon , l arabinose operon , terminator (solar) , escherichia coli , gal operon , gene , promoter , microbiology and biotechnology , gene expression , ionosphere , linguistics , philosophy , physics , astronomy
Summary The silent bgl operon of Escherichia coli is activated by spontaneous mutations that derepress its promoter. In addition, expression depends on specific transcriptional antitermination within the operon by the antiterminator protein BglG. Here, we show that BglG‐mediated antitermination limits expression of the bgl operon when the cellular transcription rate is low. The expression levels of chromosomally encoded activated bgl operon alleles are low but increase significantly when BglG protein is provided in trans or when the expression is rendered inde‐pendent of BglG‐mediated antitermination by mutation of the terminator. Plasmid‐encoded activated bgl operon alleles are expressed at high levels. Moreover, a moderate (threefold) further increase in the transcription rate of chromosomally encoded activated bgl operon alleles in an rpoS mutant can result in high (up to 50‐fold increased) expression levels. These data show that the expression of the bgl operon does not correlate linearly with its cellular transcription rate. Moderate differences in the transcription initiation rate are amplified post‐transcriptionally into large changes in the expression level of the operon by the requirement of a threshold for BglG‐mediated antitermination. Implications for bgl operon regulation by global regulators H‐NS, RpoS and others are discussed.