The antisense RNA As1_flv4 in the Cyanobacterium Synechocystis sp. PCC 6803 prevents premature expression of the flv4-2 operon upon shift in inorganic carbon supply.
The antisense RNA As1_flv4 in the Cyanobacterium Synechocystis sp. PCC 6803 prevents premature expression of the flv4-2 operon upon shift in inorganic carbon supply.
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DOI：
10.1074/jbc.m112.391755
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发表时间：
2012-09-28
期刊：
影响因子：
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通讯作者：
Aro EM
中科院分区：
文献类型：
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作者：
Eisenhut M;Georg J;Klähn S;Sakurai I;Mustila H;Zhang P;Hess WR;Aro EM
背景： flv4-2 操纵子编码的黄二铁蛋白对光系统 II 具有光保护作用，但其表达调节仍然是个谜。结果：flv4-2的表达由NdhR和反义RNA As1_flv4共同控制，而As1_flv4由AbrB样因子控制。结论：As1_flv4 提供了防止过早表达的安全阈值。意义：控制光合作用光保护的调控网络非常复杂。天然顺式反义转录本的功能相关性大多未知。在这里，我们表征了三种反义RNA和一种基因间编码的非编码RNA与操纵子的关联，该操纵子在低碳条件下蓝藻集胞藻属光系统II的光保护中发挥着至关重要的作用。 PCC 6803。蓝细菌响应细胞从高碳水平向低水平无机碳 (Ci) 的转变而表现出强烈的基因表达动态，但其调节机制知之甚少。集胞藻中上调最多的基因是 flv4、sll0218 和 flv2，它们组织在 flv4-2 操纵子中。在光氧化应激条件下，该操纵子编码的黄二铁蛋白开辟了一条替代的电子转移途径，可能从光系统 II 中的 QB 位点开始。我们对从高碳转移到低碳的细胞的表达分析表明，flv4-2操纵子mRNA和flv4的一种反义RNA（称为As1_flv4）的转录物积累呈负相关。 As1_flv4 的过度表达导致 flv4-2 mRNA 减少。 as1_flv4 的启动子活性受到 Ci 限制的瞬时刺激，并受到 AbrB 样转录调节因子 Sll0822 的负向调节，而 flv4-2 操纵子则受到转录因子 NdhR 的正向调节。结果表明，严格调控的反义 RNA As1_flv4 在 Ci 条件变化后的早期阶段建立了 flv4-2 表达的瞬时阈值。因此，它可以防止 flv4-2 操纵子不利地合成蛋白质。
Background: Flavodiiron proteins encoded by the flv4-2 operon are photoprotective for photosystem II, but their regulation of expression has remained enigmatic. Results: Expression of flv4-2 is controlled jointly by NdhR and the antisense RNA As1_flv4, whereas As1_flv4 is controlled by an AbrB-like factor. Conclusion: As1_flv4 provides a safety threshold preventing premature expression. Significance: Regulatory networks controlling photosynthetic photoprotection are highly complex. The functional relevance of natural cis-antisense transcripts is mostly unknown. Here we have characterized the association of three antisense RNAs and one intergenically encoded noncoding RNA with an operon that plays a crucial role in photoprotection of photosystem II under low carbon conditions in the cyanobacterium Synechocystis sp. PCC 6803. Cyanobacteria show strong gene expression dynamics in response to a shift of cells from high carbon to low levels of inorganic carbon (Ci), but the regulatory mechanisms are poorly understood. Among the most up-regulated genes in Synechocystis are flv4, sll0218, and flv2, which are organized in the flv4-2 operon. The flavodiiron proteins encoded by this operon open up an alternative electron transfer route, likely starting from the QB site in photosystem II, under photooxidative stress conditions. Our expression analysis of cells shifted from high carbon to low carbon demonstrated an inversely correlated transcript accumulation of the flv4-2 operon mRNA and one antisense RNA to flv4, designated as As1_flv4. Overexpression of As1_flv4 led to a decrease in flv4-2 mRNA. The promoter activity of as1_flv4 was transiently stimulated by Ci limitation and negatively regulated by the AbrB-like transcription regulator Sll0822, whereas the flv4-2 operon was positively regulated by the transcription factor NdhR. The results indicate that the tightly regulated antisense RNA As1_flv4 establishes a transient threshold for flv4-2 expression in the early phase after a change in Ci conditions. Thus, it prevents unfavorable synthesis of the proteins from the flv4-2 operon.