Biogenesis of Energy-Yielding ATP Synthase Systems in Crops

在植物产能线粒体F_1F_0ATPase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亚基基因的一部分组成了参与同源重组的重复序列，而F_0-9亚基基因位于F_1基因上游2.1kb的相反方向。结果表明，这两个基因都是从多个启动子位点转录而来的。我们对构成甘薯根线粒体F_1ATPase的6个亚基进行了纯化，并测定了5个核编码亚基的N-末端氨基酸序列。将这些序列与已知的氨基酸序列进行比较，我们可以确定这些亚基中除一个亚基外的所有亚基都与其他生物的F_1F_0ATPase亚基一致。由此推断，植物线粒体F_1在F_1ATPA的洗脱中处于独特的位置。我们克隆了甘薯F_1亚基的全长cDNA。由DNA序列推导出的-亚基前体氨基酸序列在成熟亚基的N-末端含有45个氨基酸前序列。甘薯F_1-成熟部分的氨基酸序列与牛线粒体OSCP和菠菜CF1-分别有36%和24%的同源性，但在N-末端的多肽区没有明显的同源性。然而，甘薯F_1前驱体的前序列富含碱性和羟基氨基酸，可以形成两亲性螺旋结构。在酵母、真菌和哺乳动物细胞中，后一种结构特征被认为对蛋白质向线粒体的运输非常重要。而CF1-的转运肽则不具有这种特性。

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.