Biogenesis of Energy-Yielding ATP Synthase Systems in Crops

植物线粒体产能酶f_1f_0atp酶亚基中，F_1-和F_0-9亚基由线粒体基因组编码。我们发现豌豆线粒体F_1-亚基基因部分构成同源重组的重复序列，F_0-9亚基基因位于F_1-基因上游2.1 kb，方向相反。这两个基因都检测到多种形式的转录本，详细的转录本定位和体外转录本盖帽表明，这两个基因都是从多个启动子位点转录的。我们纯化了构成甘薯根线粒体F_1ATPase的6个亚基，并确定了5个核编码亚基的n端氨基酸序列。将这些序列与已知的氨基酸序列进行比较，我们可以识别出这些亚基中除了一个-亚基之外的所有亚基与其他生物体的f_1f_0atp酶亚基的对应关系。由此推断的亚基对应关系表明，植物线粒体F_1在F_1 atp酶的进化过程中处于独特的位置。我们克隆了甘薯F_1-亚基的全长cdna。从DNA序列推断-亚基前体的氨基酸序列在成熟亚基的n端含有45个氨基酸的前体序列。甘薯F_1-成熟部分的氨基酸序列与牛线粒体OSCP和菠菜CF_1-的同源性分别为36%和24%，但在n端多余肽区未观察到明显的序列同源性。而甘薯F_1-前体序列富含碱性和羟基氨基酸，可形成两亲性螺旋结构。后一种结构特征被认为是酵母、真菌和哺乳动物细胞中蛋白质转运到线粒体的重要因素。另一方面，CF_1-的传递肽则不具有这种性质。

Among subunits of energy-yielding mitochondrial F_1F_0ATPase from plant, F_1- and F_0-9 subunits are encoded by mitochondrial genome. We found that part of pea mitochondrial F_1- subunit gene constitute a repeat sequence involced in homologous recombination, and F_0-9 subunit gene is located 2.1 kb upstream of F_1- gene in an opposite direction. Multiple forms of transcripts were deteced for both of these genes, and datailed transcript mapping and in vitro capping of transcripts suggest that both of these two genes are transcribed from multiple promoter sites.We have purified all of the 6 subunits which constitute the sweet potato root mitochondrial F_1ATPase, and determined N-terminal amino acid sequences of 5 nuclear-encoded subunits. Comparison of these sequences with known amino acid sequencess, we could identify correspondence of all but one, -subunit, of these subunits to F_1F_0ATPase subunits from other organisms. The subunit correspondences thus deduced place plant mitochondrial F_1 at an unique position in the evulution of F_1ATPase.We have cloned full-length cDNAs for the sweet potato F_1- subunit. The amino acid sequence of -subuit precursor deduced from DNA sequence contained 45 amino acid pre-sequence at the N-terminus of the mature subunit. Although the amino acid sequence of the mature part of sweet potato F_1- showed 36 and 24 % homologies with the bovine mitochondrial OSCP and spinach CF_1- , respectively, noobvious sequence homologies in the N-terminal extra peptide region were observed. However, the presequence of the sweet potato F_1- precursor is enriched with basic and hydroxyl amino acids and it can form amphiphilic helical structure. The latter structural feature has been inplied to be inportant for transport of proteins into mitochondria in yeast, fungal and mammalian cells. On the other hand, the transit peptide of the CF_1- does not show this property.