期刊
MOLECULAR MICROBIOLOGY
卷 75, 期 3, 页码 637-657出版社
WILEY
DOI: 10.1111/j.1365-2958.2009.06977.x
关键词
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资金
- BBSRC [45/P10982]
- Royal Society
- Reading University Endowment Trust
FtnA is the major iron-storage protein of Escherichia coli accounting for <= 50% of total cellular iron. The FtnA gene (ftnA) is induced by iron in an Fe2+-Fur-dependent fashion. This effect is reportedly mediated by RyhB, the Fe2+-Fur-repressed, small, regulatory RNA. However, results presented here show that ftnA iron induction is independent of RyhB and instead involves direct interaction of Fe2+-Fur with an 'extended' Fur binding site (containing five tandem Fur boxes) located upstream (-83) of the ftnA promoter. In addition, H-NS acts as a direct repressor of ftnA transcription by binding at multiple sites (I-VI) within, and upstream of, the ftnA promoter. Fur directly competes with H-NS binding at upstream sites (II-IV) and consequently displaces H-NS from the ftnA promoter (sites V-VI) which in turn leads to derepression of ftnA transcription. It is proposed that H-NS binding within the ftnA promoter is facilitated by H-NS occupation of the upstream sites through H-NS oligomerization-induced DNA looping. Consequently, Fur displacement of H-NS from the upstream sites prevents cooperative H-NS binding at the downstream sites within the promoter, thus allowing access to RNA polymerase. This direct activation of ftnA transcription by Fe2+-Fur through H-NS antisilencing represents a new mechanism for iron-induced gene expression.
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