A nucleus-encoded maize protein with sigma factor activity accumulates in mitochondria and chloroplasts
A nucleus-encoded maize protein with sigma factor activity accumulates in mitochondria and chloroplasts
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DOI：
10.1046/j.1365-313x.2002.01344.x
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发表时间：
2002-07-01
期刊：
影响因子：
7.2
通讯作者：
Allison, LA
中科院分区：
文献类型：
--
作者：
Beardslee, TA;Roy-Chowdhury, S;Allison, LA
植物含有核基因家族，编码与真细菌主要sigma因子相关的蛋白质。由于sigma因子在转录中起作用，植物蛋白被推测或证明与叶绿体的真细菌样RNA聚合酶有关。在玉米中，已经报道了5个sig cDNA序列，其中4个产物与预测的一样存在于质体中。然而，体外叶绿体导入分析和计算机算法对第五种蛋白ZmSig2B给出了模糊的结果。与其他玉米sigma因子不同，ZmSig2B在发育中的幼苗叶片以及根和黄化组织中表达。为了确定ZmSig2B的亚细胞位置，我们现在使用免疫印迹分析来表明它与线粒体和质体共同纯化。它的NH2末端153个氨基酸，翻译融合到绿色荧光蛋白（GFP）上，将绿色荧光蛋白靶向到轰击玉米叶片的叶绿体和线粒体。ZmSig2B在玉米线粒体转录提取物中的存在支持了其在线粒体转录中的假定作用。ZmSig2B也表现出叶绿体sigma因子的预期特性：重组ZmSig2B与叶绿体启动子结合，与大肠杆菌核心RNA聚合酶结合后，在体外启动转录。因此，ZmSig2B是一种不寻常的核编码sigma因子，似乎在叶绿体和线粒体中都起作用。
Plants contain nuclear gene families that encode proteins related to the principal sigma factors of eubacteria. As sigma factors function in transcription, the plant proteins have been presumed or demonstrated to associate with the eubacteria-like RNA polymerase of chloroplasts. In maize, five sig cDNA sequences have been reported, and four of the products are present in plastids as predicted. However, in vitro chloroplast import assays and computer algorithms gave ambiguous results with the fifth protein, ZmSig2B. Unlike the other maize sigma factors, ZmSig2B is expressed throughout developing seedling leaves, as well as in roots and etiolated tissues. To determine the subcellular location of ZmSig2B, we have now used immunoblot assays to show that it co-purifies with both mitochondria and plastids. Its NH2 -terminal 153 amino acids, translationally fused to green fluorescent protein (GFP), targeted GFP to chloroplasts and mitochondria in bombarded maize leaves. A putative role for ZmSig2B in mitochondrial transcription is supported by its presence in a maize mitochondrial transcription extract. ZmSig2B also exhibits the expected properties of a chloroplast sigma factor: recombinant ZmSig2B binds to a chloroplast promoter and initiates transcription in vitro when combined with Escherichia coli core RNA polymerase. Therefore ZmSig2B is an unusual nucleus-encoded sigma factor that appears to function in both chloroplasts and mitochondria.