Choi S B, Wang C, Muench D G, Ozawa K, Franceschi V R, Wu Y, Okita T W
Institute of Biological Chemistry, Washington State University, Pullman 99164, USA.
Nature. 2000 Oct 12;407(6805):765-7. doi: 10.1038/35037633.
Rice seeds, a rich reserve of starch and protein, are a major food source in many countries. Unlike the seeds of other plants, which typically accumulate one major type of storage protein, rice seeds use two major classes, prolamines and globulin-like glutelins. Both storage proteins are synthesized on the endoplasmic reticulum (ER) and translocated to the ER lumen, but are then sorted into separate intracellular compartments. Prolamines are retained in the ER lumen as protein bodies whereas glutelins are transported and stored in protein storage vacuoles. Mechanisms responsible for the retention of prolamines within the ER lumen and their assembly into intracisternal inclusion granules are unknown, but the involvement of RNA localization has been suggested. Here we show that the storage protein RNAs are localized to distinct ER membranes and that prolamine RNAs are targeted to the prolamine protein bodies by a mechanism based on RNA signal(s), a process that also requires a translation initiation codon. Our results indicate that the ER may be composed of subdomains that specialize in the synthesis of proteins directed to different compartments of the plant endomembrane system.
水稻种子富含淀粉和蛋白质，是许多国家的主要食物来源。与其他植物的种子不同，其他植物种子通常积累一种主要类型的贮藏蛋白，而水稻种子利用两种主要类型，即醇溶蛋白和类球蛋白谷蛋白。这两种贮藏蛋白均在内质网（ER）上合成并转运至内质网腔，但随后被分选到不同的细胞内区室。醇溶蛋白作为蛋白体保留在内质网腔中，而谷蛋白则被运输并贮藏在蛋白贮藏液泡中。负责将醇溶蛋白保留在内质网腔并将其组装成内质网池内包涵体颗粒的机制尚不清楚，但有人提出RNA定位参与其中。在这里，我们表明贮藏蛋白RNA定位于不同的内质网膜，并且醇溶蛋白RNA通过基于RNA信号的机制靶向醇溶蛋白体，这一过程也需要翻译起始密码子。我们的结果表明，内质网可能由专门用于合成导向植物内膜系统不同区室的蛋白质的亚结构域组成。
