Induction of the ferritin gene (ftnA) of Escherichia coli by Fe(2+)-Fur is mediated by reversal of H-NS silencing and is RyhB independent.
FtnA is the major iron-storage protein of Escherichia coli accounting for < or = 50% of total cellular iron. The FtnA gene (ftnA) is induced by iron in an Fe(2+)-Fur-dependent fashion. This effect is reportedly mediated by RyhB, the Fe(2+)-Fur-repressed, small, regulatory RNA. However, results presented here show that ftnA iron induction is independent of RyhB and instead involves direct interaction of Fe(2+)-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 Fe(2+)-Fur through H-NS antisilencing represents a new mechanism for iron-induced gene expression.
Nandal
Anjali
A
School of Biological Sciences, University of Reading, Whiteknights, Reading RG6 6AJ, UK.
Huggins
Cerys C O
CC
Woodhall
Mark R
MR
McHugh
Jonathan
J
Rodríguez-Quiñones
Francisco
F
Quail
Michael A
MA
Guest
John R
JR
Andrews
Simon C
SC
D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000378:metabolism; D005293:Ferritins / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D005798:Genes, Bacterial; D007501:Iron / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D022661:RNA, Untranslated / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D043244:Ribonuclease III / Q000378:metabolism
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D022661:RNA, Untranslated; D012097:Repressor Proteins; C068477:ferric uptake regulating proteins, bacterial; C534454:ferritin A, E coli; D005293:Ferritins; D007501:Iron; D043244:Ribonuclease III