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GadX/GadW‐dependent regulation of the Escherichia coli acid fitness island: transcriptional control at the gadY–gadW divergent promoters and identification of four novel 42 bp GadX/GadW‐specific binding sites
Author(s) -
Tramonti Angela,
De Canio Michele,
De Biase Daniela
Publication year - 2008
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 - 10.1111/j.1365-2958.2008.06458.x
Subject(s) - biology , operon , promoter , rpos , transcription (linguistics) , genetics , gene , dna footprinting , escherichia coli , transcriptional regulation , consensus sequence , binding site , conserved sequence , transcription factor , microbiology and biotechnology , peptide sequence , gene expression , linguistics , philosophy
Summary Escherichia coli has the remarkable ability to resist severe acid stress for several hours. With the notable exception of the gadBC operon, the most important genes involved in acid resistance are present within the acid fitness island (AFI), a 15 kb H‐NS‐repressed and RpoS‐controlled genome region. The AraC/XylS‐like transcriptional regulators GadX and GadW are also encoded within this region. In this article, we show that gadW transcription occurs from two native promoters, which are affected by the transcription of the divergently transcribed and GadX‐dependent gadY small RNA, and from the gadX promoter. The gadXW dicistronic transcript is subjected to post‐transcriptional processing in which GadY is involved. In contrast, gadW transcription negatively affects gadY transcription. By aligning the GadX/GadW binding site on the gadY promoter with the GadX/GadW binding sites previously identified in the gadA and gadBC 5′ regulatory regions, we generated a 42 bp GadX/GadW consensus sequence. DNase I footprinting analyses confirmed that a 42 bp GadX/GadW binding site, which matched the consensus sequence 5′‐WANDNCTDWTWKTRAYATWAWMATG KCTGATNTTTWYNTYAK‐3′, is also present in the regulatory region of the slp‐yhiF , hdeAB and gadE‐mtdEF operons, all of which belong to the AFI. The presence of five GadX/GadW‐specific binding sites in the AFI suggests that GadX and GadW may act as H‐NS counter‐silencers.