Guanosine tetra- and pentaphosphate synthase activity in chloroplasts of a higher plant: association with 70S ribosomes and inhibition by tetracycline.
Guanosine tetra- and pentaphosphate synthase activity in chloroplasts of a higher plant: association with 70S ribosomes and inhibition by tetracycline.
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DOI：
10.1093/nar/gkh916
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发表时间：
2004
影响因子：
14.9
通讯作者：
K. Kasai;T. Kanno;Y. Endo;K. Wakasa;Y. Tozawa
中科院分区：
文献类型：
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作者：
K. Kasai;T. Kanno;Y. Endo;K. Wakasa;Y. Tozawa
叶绿体具有细菌型的转录和翻译系统。在鉴定莱茵衣藻基因编码的RelA-SpoT同源物（RSH），催化鸟苷四或五磷酸[（p）ppGpp]的合成的基础上，我们以前提出的叶绿体遗传系统中的严格控制的操作。虽然RSH基因也已在几种高等植物中被鉴定，但其编码的酶的活性及其在叶绿体中的作用模式仍不清楚。我们现在已经表征了从豌豆（Pisum sativum）制备的叶绿体提取物的内在（p）ppGpp合酶活性。超离心分级表明，（p）ppGpp合酶活性的叶绿体基质提取物的抑制活性与70 S核糖体。此外，这种酶活性被四环素抑制，提取物的肽延伸活性也是如此。大肠杆菌和豌豆叶绿体的rRNA分子之间的结构比较发现，推定的四环素结合位点的保守性。这些观察结果表明，在高等植物的叶绿体中存在核糖体相关的（p）ppGpp合酶活性，进一步暗示（p）ppGpp在叶绿体的遗传系统中类似于在细菌中起作用的系统。
Chloroplasts possess bacterial-type systems for transcription and translation. On the basis of the identification of a Chlamydomonas reinhardtii gene encoding a RelA-SpoT homolog (RSH) that catalyzes the synthesis of guanosine tetra- or pentaphosphate [(p)ppGpp], we have previously suggested the operation of stringent control in the chloroplast genetic system. Although RSH genes have also been identified in several higher plants, the activities of the encoded enzymes and their mode of action in chloroplasts have remained uncharacterized. We have now characterized the intrinsic (p)ppGpp synthase activity of chloroplast extracts prepared from pea (Pisum sativum). Fractionation by ultracentrifugation suggested that the (p)ppGpp synthase activity of a translationally active chloroplast stromal extract was associated with 70S ribosomes. Furthermore, this enzymatic activity was inhibited by tetracycline, as was the peptide elongation activity of the extract. Structural comparisons between rRNA molecules of Escherichia coli and pea chloroplasts revealed the conservation of putative tetracycline-binding sites. These observations demonstrate the presence of a ribosome-associated (p)ppGpp synthase activity in the chloroplasts of a higher plant, further implicating (p)ppGpp in a genetic system of chloroplasts similar to that operative in bacteria.