The Bradyrhizobium japonicum Irr protein is a transcriptional repressor with high-affinity DNA-binding activity.
The Bradyrhizobium japonicum Irr protein is a transcriptional repressor with high-affinity DNA-binding activity.
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Bradyrhizobium japonicum Irr 蛋白是一种具有高亲和力 DNA 结合活性的转录阻遏蛋白。
DOI：
10.1128/jb.00495-08
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发表时间：
2008
影响因子：
3.2
通讯作者：
O'Brian,MarkR
中科院分区：
文献类型：
--
作者：
Sangwan,Indu;Small,SandraK;O'Brian,MarkR
The Irr protein is a global regulator of iron homeostasis inBradyrhizobium japonicum, and a subset of genes within the Irr regulon are negatively controlled under iron limitation. However, repressor function, high-affinity DNA binding in vitro, or promoter occupancy in vivo of Irr for a negatively regulated gene has not been demonstrated. Here, we show that the blr7895 and bll6680 genes are negatively regulated by Irr as determined by derepression of transcript levels in iron-limited cells of anirrmutant strain. Electrophoretic gel mobility shift analysis showed that a component in extracts of wild-type cells grown under iron limitation bound the iron control elements (ICE) within the promoters of blr7895 and bll6680 identified previously (G. Rudolph, G. Semini, F. Hauser, A. Lindemann, M. Friberg, H. Hennecke, and H. M. Fischer, J. Bacteriol. 188:733-744, 2006). Binding was not observed with extracts of cells from the parent strain grown under high iron conditions or with those from anirrmutant. Furthermore, gel mobility supershift experiments identified Irr as a component of the binding complex. Purified recombinant Irr bound to ICE DNA with high affinity in the presence of divalent metal, withKdvalues of 7 to 19 nM, consistent with a physiological role for Irr as a transcriptional regulator. In addition, in vitro transcription initiated from the blr7895 promoter was inhibited by Irr. Whole-cell cross-linking and immunoprecipitation experiments showed that Irr occupies the promoters of blr7895 and bll6680 in vivo in an iron-dependent manner. The findings demonstrate that Irr is a transcriptional repressor that binds DNA with high affinity.
