Jackson-Constan D, Keegstra K
Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824-1312, USA.
Plant Physiol. 2001 Apr;125(4):1567-76. doi: 10.1104/pp.125.4.1567.
The process of protein import into plastids has been studied extensively using isolated pea (Pisum sativum) chloroplasts. As a consequence, virtually all of the known components of the proteinaceous apparatus that mediates import were originally cloned from pea. With the recent completion of the Arabidopsis genome sequencing project, it is now possible to identify putative homologs of the import components in this species. Our analysis has revealed that Arabidopsis homologs with high sequence similarity exist for all of the pea import complex subunits, making Arabidopsis a valid model for further study of this system. Multiple homologs can be identified for over one-half of the components. In all but one case it is known that more than one of the putative isoforms for a particular subunit are expressed. Thus, it is possible that multiple types of import complexes are present within the same cell, each having a unique affinity for different chloroplastic precursor proteins, depending upon the exact mix of isoforms it contains. Sequence analysis of the putative Arabidopsis homologs for the chloroplast protein import apparatus has revealed many questions concerning subunit function and evolution. It should now be possible to use the genetic tools available in Arabidopsis, including the generation of knockout mutants and antisense technology, to address these questions and learn more about the molecular functions of each of the components during the import process.
利用分离的豌豆（Pisum sativum）叶绿体，对蛋白质导入质体的过程进行了广泛研究。因此，介导导入的蛋白质装置中几乎所有已知成分最初都是从豌豆中克隆出来的。随着拟南芥基因组测序项目的近期完成，现在有可能在该物种中鉴定出导入成分的推定同源物。我们的分析表明，豌豆导入复合体的所有亚基在拟南芥中都存在具有高度序列相似性的同源物，这使得拟南芥成为进一步研究该系统的有效模型。超过一半的成分可以鉴定出多个同源物。除了一种情况外，已知特定亚基的多个推定异构体都有表达。因此，同一细胞内可能存在多种类型的导入复合体，每种复合体对不同的叶绿体前体蛋白具有独特的亲和力，这取决于其所含异构体的确切组合。对叶绿体蛋白质导入装置的拟南芥推定同源物的序列分析揭示了许多有关亚基功能和进化的问题。现在应该可以利用拟南芥中可用的遗传工具，包括产生基因敲除突变体和反义技术，来解决这些问题，并更多地了解导入过程中每个成分的分子功能。
