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禽博德特氏菌中rhuIR-bhuRSTUV血红素获取基因座的转录调控

Transcriptional control of the rhuIR-bhuRSTUV heme acquisition locus in Bordetella avium.

作者信息

King Natalie D, Kirby Amy E, Connell Terry D

机构信息

Witebsky Center for Microbial Pathogenesis and Immunology, University at Buffalo, State University of New York, 138 Farber Hall, 3435 Main St., Buffalo, NY 14214, USA.

出版信息

Infect Immun. 2005 Mar;73(3):1613-24. doi: 10.1128/IAI.73.3.1613-1624.2005.

Abstract

Iron (Fe) is an essential nutrient for most bacterial pathogens. In these organisms, a variety of regulatory systems that respond to specific Fe complexes found within their vertebrate hosts have evolved. In Bordetella avium, the heme utilization locus encoded by rhuIR-bhuRSTUV mediates efficient acquisition of Fe from heme and hemoproteins. Control of bhuRSTUV expression is promulgated at two levels. When Fe is abundant, expression is repressed in a Fur-dependent manner which is partially relieved when Fe is limiting. In the presence of heme or hemoproteins, expression of the bhuRSTUV operon is induced via a three-component signal transduction cascade composed of RhuI, RhuR, and BhuR. Herein, we report the identification of two promoters (PrhuI and PbhuR) that control expression of the rhuIR-bhuRSTUV cluster. Primer extension analysis identified the transcriptional start site of PrhuI within a putative Fur box. Transcriptional initiation of PbhuR mapped within the rhuR-bhuR intergenic region. Maximal transcription from PbhuR required Fe-limiting conditions, the presence of heme (or hemoglobin), and rhuI; however, analysis of transcripts produced from the rhuIR-bhuRSTUV locus revealed a pattern of low-level bhuR transcription in the absence of heme which originated from both PbhuR and PrhuI. Transcription from PrhuI was repressed by Fe in the presence of fur and somewhat enhanced by the addition of hemin to Fe-limited media. The nature of this hemin-associated PrhuI stimulation was rhuI independent and therefore not induced by heme via the BhuR-RhuR-RhuI signal cascade. Fe also repressed transcription from PbhuR in a fur-dependent manner; however, activation from this promoter, in the presence or absence of heme, did not occur without rhuI.

摘要

铁(Fe)是大多数细菌病原体必需的营养素。在这些生物体中,已经进化出多种响应其脊椎动物宿主中特定铁复合物的调节系统。在鸟博德特氏菌中,由rhuIR-bhuRSTUV编码的血红素利用位点介导了从血红素和血红蛋白中高效获取铁。bhuRSTUV表达的控制在两个水平上进行。当铁丰富时,表达以铁摄取调节蛋白(Fur)依赖的方式被抑制,当铁有限时部分解除抑制。在存在血红素或血红蛋白的情况下,bhuRSTUV操纵子的表达通过由RhuI、RhuR和BhuR组成的三组分信号转导级联被诱导。在此,我们报告了控制rhuIR-bhuRSTUV簇表达的两个启动子(PrhuI和PbhuR)的鉴定。引物延伸分析确定了PrhuI的转录起始位点在一个假定的Fur框内。PbhuR的转录起始定位在rhuR-bhuR基因间区域内。来自PbhuR的最大转录需要铁限制条件、血红素(或血红蛋白)的存在以及rhuI;然而,对rhuIR-bhuRSTUV位点产生的转录本的分析揭示了在没有血红素的情况下低水平bhuR转录的模式,其起源于PbhuR和PrhuI。在存在fur的情况下,Fe抑制PrhuI的转录,并且在铁限制培养基中添加血红素会使其有所增强。这种与血红素相关的PrhuI刺激的性质不依赖于rhuI,因此不是由血红素通过BhuR-RhuR-RhuI信号级联诱导的。Fe也以fur依赖的方式抑制PbhuR的转录;然而,在有或没有血红素的情况下,没有rhuI就不会发生来自该启动子的激活。

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引用本文的文献

本文引用的文献

1
Integration of environmental signals controls expression of Bordetella heme utilization genes.
J Bacteriol. 2004 Feb;186(4):938-48. doi: 10.1128/JB.186.4.938-948.2004.
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J Bacteriol. 2003 Feb;185(3):909-17. doi: 10.1128/JB.185.3.909-917.2003.
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J Bacteriol. 2001 Jul;183(14):4278-87. doi: 10.1128/JB.183.14.4278-4287.2001.
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Fur-independent regulation of iron metabolism by Irr in Bradyrhizobium japonicum.
Microbiology (Reading). 2000 Mar;146 ( Pt 3):669-676. doi: 10.1099/00221287-146-3-669.
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J Bacteriol. 1999 Oct;181(20):6223-9. doi: 10.1128/JB.181.20.6223-6229.1999.

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