Horwich A L, Kalousek F, Fenton W A, Furtak K, Pollock R A, Rosenberg L E
J Cell Biol. 1987 Aug;105(2):669-77. doi: 10.1083/jcb.105.2.669.
The cytoplasmically synthesized precursor of the mitochondrial matrix enzyme, ornithine transcarbamylase (OTC), is targeted to mitochondria by its NH2-terminal leader peptide. We previously established through mutational analysis that the midportion of the OTC leader peptide is functionally required. In this article, we report that study of additional OTC precursors, altered in either a site-directed or random manner, reveals that (a) the midportion, but not the NH2-terminal half, is sufficient by itself to direct import, (b) the functional structure in the midportion is unlikely to be an amphiphilic alpha-helix, (c) the four arginines in the leader peptide contribute collectively to import function by conferring net positive charge, and (d) surprisingly, proteolytic processing of the leader peptide does not require the presence of a specific primary structure at the site of cleavage, in order to produce the mature OTC subunit.
线粒体基质酶鸟氨酸转氨甲酰酶（OTC）在细胞质中合成的前体，通过其氨基末端前导肽靶向线粒体。我们之前通过突变分析确定OTC前导肽的中部在功能上是必需的。在本文中，我们报告称，对以定点或随机方式改变的其他OTC前体的研究表明：（a）中部而非氨基末端的一半本身就足以指导导入；（b）中部的功能结构不太可能是两亲性α螺旋；（c）前导肽中的四个精氨酸通过赋予净正电荷共同促进导入功能；（d）令人惊讶的是，前导肽的蛋白水解加工在切割位点不需要特定的一级结构存在，就能产生成熟的OTC亚基。
