Cell cycle control of secondary endosymbionts

隐单胞虫是由异养真核生物吞噬真核藻类细胞而进化而来的。在细胞内的生活过程中，共生体被还原成一个多膜结合的质体（复合质体）。然而，与其他具有类似系统发育起源和复杂质体的生物（如顶复合体）相比，隐孢子虫仍然含有真核共生体的还原核，称为核形态。核形态的分裂先于细胞核的分裂，并受宿主的控制。在我们的国际核形态基因组计划中，我们扫描了核形态中编码细胞周期因子的基因。因此，我们能够预见哪些细胞周期成分是由宿主补充的。这些成分是寄主调控共生体细胞周期的分子基础。在我们的项目中，我们将分离涉及S-和G2-M-期的因素，并表征它们的拓扑信号及其调控。这将首次提供负责蛋白质在复杂质体的前两层膜上运输的信号。由于拓扑信号是蛋白质进入复杂质体的标志，它们的知识将通过筛选顶质体数据库来识别定位在顶质体膜上的蛋白质。

Cryptomonads evolved by the engulfment of a eukaryotic algal cell by a heterotrophic eukaryote. In the course of intracellular lifestyle, the symbionts are reduced to a multi-membrane bounded plastid (complex plastid). However, in comparison to other organisms with similar phylogenetic origin and complex plastids (e.g. the Apicomplexa), cryptomonads still contain the reduced nucleus of the eukaryotic symbiont, called the nucleomorph. The division of the nucleomorph preceeds those of the cell nucleus and is under the control of the host. In the course of our international nucleomorph genome project we have scanned the nucleomorph for genes encoding cell cycle factors. Thus, we are able to foresee which cell cycle components are supplemented by the host. These components are the molecular basis for the regulation of the symbiont´s cell cycle by the host. In our project we will isolate factors involved in the S- and G2-M- phases and characterize their topogenic signals as well as their regulation. This will offer for the first time the signals which are responsible for protein transport across the first two membranes of a complex plastid. As topogenic signals are markers for protein import into complex plastids, their knowledge will be used to identify proteins localized in the apicoplast membranes by screening the Apicomplexa databases.