Translational control of small heat shock genes in mesophilic and thermophilic cyanobacteria by RNA thermometers.
Translational control of small heat shock genes in mesophilic and thermophilic cyanobacteria by RNA thermometers.
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DOI：
10.4161/rna.28648
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发表时间：
2014
期刊：
影响因子：
4.1
通讯作者：
Narberhaus F
中科院分区：
文献类型：
--
作者：
Cimdins A;Klinkert B;Aschke-Sonnenborn U;Kaiser FM;Kortmann J;Narberhaus F
蓝细菌是一种异质性的产氧、光合原核生物门。它们容易受到各种应激条件，如热，盐或光胁迫，所有诱导蓝藻热休克反应（HSR）。蓝藻小分子热激蛋白（small heat shock proteins，sHsps）在逆境条件下能保持类囊体膜的完整性，从而保护光合作用机制。在集胞藻（Synechocystis sp PCC 6803）中，sHsp Hsp 17的合成受hsp 17 mRNA 5′-非翻译区（5′-UTR）的RNA温度计（RNAthermometer，RNAT）调控。RNAT是直接的温度传感器，控制许多细菌热休克和毒力基因的表达。它们通过碱基配对在低温下阻碍翻译，从而阻断核糖体与mRNA的接触。 为了探索RNAT作用的温度范围，我们研究了嗜温和嗜热蓝藻sHsp基因上游的各种RNAT候选物。嗜温蓝藻鱼腥藻和念珠藻染色体编码两个sHsps。报告基因的研究表明，RNAT介导的转录后调控的shsp表达在这两种生物体。对两个A. variabilis候选人揭示了两个新的RNAT类型。第一个是avashort，主要通过掩蔽AUG翻译起始密码子来调节翻译。第二，具有延长的初始发夹，因此命名为avalong，大概是利用复杂的三级相互作用。嗜热菌细长热聚球藻（Thermosynechococcuselongatus）小分子热激基因hspA的5′-UTR具有较长的二级结构。结构探测显示，核糖体结合位点在低于55 °C的温度下被阻断。本研究的结果表明，蓝藻通常使用RNAT来控制其小的热休克基因的表达。
Cyanobacteria constitute a heterogeneous phylum of oxygen-producing, photosynthetic prokaryotes. They are susceptible to various stress conditions like heat, salt, or light stress, all inducing the cyanobacterial heat shock response (HSR). Cyanobacterial small heat shock proteins (sHsps) are known to preserve thylakoid membrane integrity under stress conditions, thereby protecting the photosynthesis machinery. In Synechocystis sp PCC 6803, synthesis of the sHsp Hsp17 is regulated by an RNA thermometer (RNAT) in the 5′-untranslated region (5′-UTR) of the hsp17 mRNA. RNATs are direct temperature sensors that control expression of many bacterial heat shock and virulence genes. They hinder translation at low temperatures by base pairing, thus blocking ribosome access to the mRNA. To explore the temperature range in which RNATs act, we studied various RNAT candidates upstream of sHsp genes from mesophilic and thermophilic cyanobacteria. The mesophilic cyanobacteria Anabaena variabilis and Nostoc sp chromosomally encode two sHsps each. Reporter gene studies suggested RNAT-mediated post-transcriptional regulation of shsp expression in both organisms. Detailed structural analysis of the two A. variabilis candidates revealed two novel RNAT types. The first, avashort, regulates translation primarily by masking of the AUG translational start codon. The second, featuring an extended initial hairpin, thus named avalong, presumably makes use of complex tertiary interaction. The 5′-UTR of the small heat shock gene hspA in the thermophile Thermosynechococcus elongatus is predicted to adopt an extended secondary structure. Structure probing revealed that the ribosome binding site was blocked at temperatures below 55 °C. The results of this study demonstrate that cyanobacteria commonly use RNATs to control expression of their small heat shock genes.