Heme may represent a major iron-source for bacteria. In the symbiotic nitrogen-fixing bacterium Ensifer meliloti 1021, iron acquisition from heme depends on the outer-membrane heme-receptor ShmR. Expression of shmR gene is repressed by iron in a RirA dependent manner while under iron-limitation its expression requires the small protein HmuP. In this work, we identified highly conserved nucleotide motifs present upstream the shmR gene. These motifs are widely distributed among Alpha and Beta Proteobacteria, and correlate with the presence of HmuP coding sequences in bacterial genomes. According to data presented in this work, we named these new motifs as HmuP-responsive elements (HPREs). In the analyzed genomes, the HPREs were always present upstream of genes encoding putative heme-receptors. Moreover, in those Alpha and Beta Proteobacteria where transcriptional start sites for shmR homologs are known, HPREs were located in the 5'UTR region. In this work we show that in E. meliloti 1021, HPREs are involved in HmuP-dependent shmR expression. Moreover, we show that changes in sequence composition of the HPREs correlate with changes in a predicted RNA secondary structure element and affect shmR gene expression.

中文翻译：

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血红素受体基因shmR的5'UTR中存在的高度保守的核苷酸基序是melsentiti中HmuP依赖的shmR表达的必需条件。

血红素可能代表细菌的主要铁源。在共生固氮细菌Ensifer meliloti 1021中，从血红素获得铁取决于外膜血红素受体ShmR。铁以RirA依赖性方式抑制shmR基因的表达，而在铁限制下其表达需要小蛋白HmuP。在这项工作中，我们确定了shmR基因上游存在的高度保守的核苷酸基序。这些基序广泛分布在Alpha和Beta变形杆菌中，并与细菌基因组中HmuP编码序列的存在相关。根据这项工作中提供的数据，我们将这些新主题命名为HmuP响应元件（HPRE）。在分析的基因组中，HPRE始终存在于编码假定的血红素受体的基因上游。此外，在已知shmR同源物转录起始位点的Alpha和Beta变形杆菌中，HPRE位于5'UTR区域。在这项工作中，我们表明，在E. meliloti 1021中，HPRE参与了HmuP依赖性shmR表达。此外，我们表明，HPREs序列组成的变化与预测的RNA二级结构元素的变化相关，并影响shmR基因表达。