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The Molybdate-Responsive Escherichia coli ModE Transcriptional Regulator Coordinates Periplasmic Nitrate Reductase (napFDAGHBC) Operon Expression with Nitrate and Molybdate Availability. Paul M. McNicholas, 2002.Expression of the Escherichia coli napFDAGHBC operon (also known as aeg46.5), which encodes the periplasmic molybdoenzyme for nitrate reduction, is increased in response to anaerobiosis and further stimulated by the addition of nitrate or to a lesser extent by nitrite to the cell culture medium . These changes are mediated by the transcription factors Fnr and NarP, respectively . Utilizing a napF-lacZ operon fusion, we demonstrate that napF gene expression is impaired in strain defective for the molybdate-responsive ModE transcription factor . This control abrogates nitrate- or nitrite-dependent induction during anaerobiosis . Gel shift and DNase I footprinting analyses establish that ModE binds to the napF promoter with an apparent Kd of about 35 nM at a position centered at -133.5 relative to the start of napF transcription . Although the ModE binding site sequence is similar to other E . coli ModE binding sites, the location is atypical, because it is not centered near the start of transcription . Introduction of point mutations in the ModE recognition site severely reduced or abolished ModE binding in vitro and conferred a modE phenotype (i.e., loss of molybdate-responsive gene expression) in vivo . In contrast, deletion of the upstream ModE region site rendered napF expression independent of modE. These findings indicate the involvement of an additional transcription factor to help coordinate nitrate- and molybdate-dependent napF expression by the Fnr, NarP, NarL, and ModE proteins . The upstream ModE regulatory site functions to override nitrate control of napF gene expression when the essential enzyme component, molybdate, is limiting in the cell environment . The ftsH Gene of the Wine Bacterium Oenococcus oeni Is Involved in Protection against Environmental Stress. Jean-Paul Bourdineaud, 2003.The wine bacterium Oenococcus oeni has to cope with harsh environmental conditions, including an acidic pH, a high alcoholic content, nonoptimal growth temperatures, and growth-inhibitory compounds such as fatty acids, phenolic acids, and tannins . We describe the characterization and cloning of the O . oeni ftsH gene, encoding a protease belonging to the ATP binding cassette protein superfamily . The O . oeni FtsH protein is closest in sequence similarity to the FtsH homologue of Lactococcus lactis . The O . oeni ftsH gene proved to be stress-responsive, since its expression increased at high temperatures or under osmotic shock . O . oeni FtsH protein function was tested in an Escherichia coli ftsH mutant strain, and consistent with the O . oeni ftsH gene expression pattern, the O . oeni FtsH protein provided protection for the E . coli ftsH mutant against heat shock . O . oeni and Bradyrhizobium japonicum FtsH proteins also triggered E . coli resistance to wine toxicity . Genes homologous to O . oeni ftsH were detected in many other lactic acid bacteria found in wine, suggesting that this type of gene constitutes a well-conserved stress-protective molecular device .
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