Li H M, Chen L J
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China.
Plant Cell. 1996 Nov;8(11):2117-26. doi: 10.1105/tpc.8.11.2117.
Most proteins in chloroplasts are encoded by the nuclear genome and synthesized in the cytosol. With the exception of most quter envelope membrane proteins, nuclear-encoded chloroplastic proteins are synthesized with N-terminal extensions that contain the chloroplast targeting information of these proteins. Most outer membrane proteins, however, are synthesized without extensions in the cytosol. Therefore, it is not clear where the chloroplastic outer membrane targeting information resides within these polypeptides. We have analyzed a chloroplastic outer membrane protein, OEP14 (outer envelope membrane protein of 14 kD, previously named OM14), and localized its outer membrane targeting and integration signal to the first 30 amino acids of the protein. This signal consists of a positively charged N-terminal portion followed by a hydrophobic core, bearing resemblance to the signal peptides of proteins targeted to the endoplasmic reticulum. However, a chimeric protein containing this signal fused to a passenger protein did not integrate into the endoplasmic reticulum membrane. Furthermore, membrane topology analysis indicated that the signal inserts into the chloroplastic outer membrane in an orientation opposite to that predicted by the "positive inside" rule.
叶绿体中的大多数蛋白质由核基因组编码并在细胞质中合成。除了大多数外膜蛋白外，核编码的叶绿体蛋白在合成时带有N端延伸序列，其中包含这些蛋白的叶绿体靶向信息。然而，大多数外膜蛋白在细胞质中合成时没有延伸序列。因此，尚不清楚叶绿体外膜靶向信息在这些多肽中的位置。我们分析了一种叶绿体外膜蛋白OEP14（14 kD的外膜蛋白，先前称为OM14），并将其外膜靶向和整合信号定位到该蛋白的前30个氨基酸。该信号由带正电荷的N端部分和随后的疏水核心组成，与靶向内质网的蛋白质的信号肽相似。然而，一种含有该信号并与乘客蛋白融合的嵌合蛋白并未整合到内质网膜中。此外，膜拓扑分析表明，该信号以与“正电荷在内”规则预测相反的方向插入叶绿体外膜。
