LEADER PEPTIDES--SUBUNITS OF MEMBRANE PROTEIN OLIGOMERS

许多整合膜蛋白在原位是异源寡聚体。 他们的 生物发生需要将不同的亚基多肽靶向于 正确的细胞内膜和它们的正确组装成一个功能 复杂. 以前的研究强调了NH 2-末端的重要性， 用于蛋白质靶向膜表面的“前导肽” 以及它们随后插入膜中。 但也使得 很清楚插入或穿过细胞膜的蛋白质 协同使用它们的“前导肽”，与可溶性 蛋白质来调节它们自身的翻译。 尽管有明显的 “前导肽”前序列的重要性，它们的命运， 处理不确定。 同样不确定的是，他们是否执行其他 在膜生物发生中起作用。 我们建议测试一个新的假设：“前导肽”的功能是 一些膜蛋白寡聚体的亚基。 这个假设已经发展到 三个最近测序的核编码多肽 酵母细胞色素c氧化酶的亚基（VII、VIIa和VIII）是同源的 已知的“前导肽”，从其他无关的，核编码的， 线粒体蛋白 我们计划1）克隆和测序结构 这三个亚单位的基因，以确定他们是否是，事实上，“领导者， “肽”衍生自较大的多肽前体， -COOH末端; 2）通过在它们的末端构建无效突变体来确定， 结构基因，如果它们是组装或功能所必需的， 全细胞色素C氧化酶;和3）鉴定与它们结合的蛋白质 如果我们发现它们是“前导肽”， 这些研究可能 鉴定了“前导肽”在膜生物发生中另一个作用， 提供了一个重要的线索，关于机制，大会 同一膜中蛋白质寡聚体的途径是协调的。

Many integral membrane proteins are hetero-oligomers in situ. Their biogenesis requires the targeting of different subunit polypeptides to the correct intracellular membrane and their proper assembly into a functional complex. Previous studies have stressed the importance of NH2-terminal "leader peptides" for both the targeting of proteins to membrane surfaces and their subsequent insertion into the membrane. They have also made clear that proteins which are inserted into or through membranes co-translationally use their "leader-peptides", in conjunction with soluble proteins, to regulate their own translation. Despite the obvious importance of "leader peptide" presequences, their fate, after being processed is uncertain. Also uncertain is whether they perform other functions in membrane biogenesis. We propose to test a new hypothesis: that "leader peptides" function as subunits in some membrane protein oligomers. This hypothesis has grown out of the finding that three recently sequenced nuclear-coded polypeptide subunits (VII, VIIa, and VIII) of yeast cytochrome c oxidase are homologous to known "leader peptides" from other, unrelated, nuclear-coded mitochondrial proteins. We plan to 1) clone and sequence the structural genes for these three subunits to determine if they are, in fact, "leader peptides" derived from larger polypeptide precursors extending from their -COOH terminus; 2) determine, by constructing null mutants in their structural genes, if they are required for the assembly or function of holocytochrome c oxidase; and 3) identify proteins with which they are contiguous should we find that they are "leader pepdides". The studies may identify another role for "leader peptides" in membrane biogenesis and provide an important clue regarding the mechanisms by which the assembly pathways of protein oligomers in the same membrane are coordinated.