Vogel H, Fischer S, Valentin K
Institute for Plant Physiology, Justus-Liebig University, Giessen, Germany.
Plant Mol Biol. 1996 Nov;32(4):685-92. doi: 10.1007/BF00020209.
Plastids possess a bacteria-like sec apparatus that is involved in protein import into the thylakoid lumen. We have analyzed one of the genes essential for this process, secY. A secY gene from the unicellular red alga Cyanidium caldarium was found to be transcriptionally active, demonstrating for the first time that secY is functional in a plastid. Unlike the situation seen in bacteria the C. caldarium gene is transcribed monocistronically, despite the fact that it is part of a large ribosomal gene cluster that resembles bacterial spc operons. A molecular phylogeny is presented for 8 plastid-encoded secY genes, four of which have not been published yet. In this analysis plastid secY genes fall into two classes. One of these, comprising of genes from multicellular red algae and Cryptophyta, clusters in a neighbour-joining tree with a cyanobacterial counterpart. Separated from the aforesaid are secY genes from Chromophyta, Glaucocystophyta and a unicellular red alga. All plastid and cyanobacterial sequences are located on the same branch, separated from bacterial homologues. We postulate that the two classes of secY genes are paralogous, i.e. their gene products are involved in different protein translocation processes. Based on this assumption a model for the evolution of the plastid sec apparatus is presented.
质体拥有一种类似于细菌的Sec转运系统，该系统参与蛋白质导入类囊体腔。我们分析了这一过程中必需的一个基因，即secY。发现单细胞红藻嗜热蓝纤维藻的一个secY基因具有转录活性，首次证明secY在质体中发挥功能。与细菌不同的是，嗜热蓝纤维藻基因以单顺反子形式转录，尽管它是一个类似于细菌spc操纵子的大型核糖体基因簇的一部分。本文给出了8个质体编码的secY基因的分子系统发育树，其中4个基因尚未发表。在该分析中，质体secY基因分为两类。其中一类由多细胞红藻和隐藻的基因组成，在邻接树中与一个蓝细菌对应基因聚类在一起。与上述基因分开的是来自褐藻、灰胞藻和一种单细胞红藻的secY基因。所有质体和蓝细菌序列位于同一分支上，与细菌同源物分开。我们推测这两类secY基因是旁系同源的，即它们的基因产物参与不同的蛋白质转运过程。基于这一假设，本文提出了质体Sec转运系统的进化模型。
