Transcription Antitermination by a Phosphorylated Response Regulator and Cobalamin-Dependent Termination at a B12 Riboswitch Contribute to Ethanolamine Utilization in Enterococcus faecalis
Transcription Antitermination by a Phosphorylated Response Regulator and Cobalamin-Dependent Termination at a B12 Riboswitch Contribute to Ethanolamine Utilization in Enterococcus faecalis
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DOI：
10.1128/jb.00217-11
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发表时间：
2011-05-01
影响因子：
3.2
通讯作者：
Perego, Marta
中科院分区：
文献类型：
--
作者：
Baker, Kris Ann;Perego, Marta
细菌利用乙醇胺（EA）作为碳和氮源的能力可能赋予细菌在人类肠道中的生存、定植和致病性优势。粪肠球菌（Enterococcus faecalis）是一种革兰氏阳性的人类共生生物，依靠双组分信号系统（TCS-17）来感知EA并调节乙醇胺利用基因的表达。在EA作为唯一碳源和钴胺素（CoB12）存在的情况下，多个启动子参与了eut基因的表达，钴胺素是酶降解过程中必不可少的辅助因子。通过体内和体外方法，本研究鉴定了在粪肠球菌eut - eutg基因间区鉴定的转录活性。该区域的两个新的启动子在体内被证明是活跃的。远端P2-1启动子与B12核糖开关相关，该开关在co12存在时终止转录。来自P2-2近端启动子的转录延伸受TCS-17 （RR17）的磷酸化形式介导的反终止调控。3'- cDNA末端快速扩增（RACE）分析终止RNA产物，可以精确鉴定参与终止/反终止的发夹环结构。这些结果揭示了B12核糖开关和RR17在eut基因表达中的作用，增加了这一调控途径的复杂性，并扩展了对革兰氏阳性生物体中转录调控可能手段的了解。
The ability of bacteria to utilize ethanolamine (EA) as a carbon and nitrogen source may confer an advantage for survival, colonization, and pathogenicity in the human intestinal tract. Enterococcus faecalis, a Gram-positive human commensal organism, depends on a two-component signaling system (TCS-17) for sensing EA and regulating the expression of the ethanolamine utilization genes. Multiple promoters participate in eut gene expression in the presence of EA as the sole carbon source and cobalamin (CoB12), an essential cofactor in the enzymatic degradation process. By means of in vivo and in vitro approaches, this study characterized the transcriptional activity identified in the eutT-eutG intergenic region of the E. faecalis eut cluster. Two novel promoters in this region were shown to be active in vivo. The distal P2-1 promoter was associated with a B12 riboswitch that terminated transcription in the presence of CoB12. Transcription elongation from the proximal P2-2 promoter was regulated by antitermination mediated by the phosphorylated form of the response regulator of TCS-17 (RR17). 3'-Rapid amplification of cDNA ends (RACE) analyses of the terminated RNA products allowed precise identification of the hairpin loop structures involved in termination/antitermination. The results uncovered the role of the B12 riboswitch and RR17 in eut gene expression, adding to the complexity of this regulatory pathway and extending the knowledge of possible means of transcription regulation in Gram-positive organisms.