Richter Uwe, Kiessling Justine, Hedtke Boris, Decker Eva, Reski Ralf, Börner Thomas, Weihe Andreas
Institut für Biologie, Humboldt-Universität, Chausseestrasse 117, Berlin, Germany.
Gene. 2002 May 15;290(1-2):95-105. doi: 10.1016/s0378-1119(02)00583-8.
Angiosperms possess a small family of phage-type RNA polymerase genes that arose by gene duplication from an ancestral gene encoding the mitochondrial RNA polymerase. We have isolated and sequenced the genes and cDNAs encoding two phage-type RNA polymerases, PpRpoT1 and PpRpoT2, from the moss Physcomitrella patens. PpRpoT1 comprises 19 exons and 18 introns, PpRpoT2 contains two additional introns. The N-terminal transit peptides of both polymerases are shown to confer dual-targeting of green fluorescent protein fusions to mitochondria and plastids. In vitro translation of the cDNAs revealed initiation of translation at two in-frame AUG start codons. Translation from the first methionine gives rise to a plastid-targeted polymerase, whereas initiation from the second methionine results in exclusively mitochondrial-targeted protein. Thus, dual-targeting of Physcomitrella RpoT is caused by and might be regulated by multiple translational starts. In phylogenetic analyses, the Physcomitrella RpoT polymerases form a sister group to all other phage-type polymerases of land plants. The two genes result from a gene duplication event that occurred independently from the one which led to the organellar polymerases with mitochondrial or plastid targeting properties in angiosperms. Yet, according to their conserved exon-intron structures they are representatives of the molecular evolutionary line leading to the RpoT genes of higher land plants.
被子植物拥有一小类噬菌体类型的RNA聚合酶基因，这些基因是由编码线粒体RNA聚合酶的祖先基因通过基因复制产生的。我们已经从苔藓小立碗藓中分离并测序了编码两种噬菌体类型RNA聚合酶PpRpoT1和PpRpoT2的基因和cDNA。PpRpoT1由19个外显子和18个内含子组成，PpRpoT2还含有另外两个内含子。两种聚合酶的N端转运肽均显示可将绿色荧光蛋白融合体双靶向到线粒体和质体。cDNA的体外翻译揭示了在两个读框内的AUG起始密码子处开始翻译。从第一个甲硫氨酸开始翻译产生一个靶向质体的聚合酶，而从第二个甲硫氨酸开始起始则仅产生靶向线粒体的蛋白质。因此，小立碗藓RpoT的双靶向是由多个翻译起始引起的，并且可能受其调控。在系统发育分析中，小立碗藓RpoT聚合酶与陆地植物的所有其他噬菌体类型聚合酶形成一个姐妹群。这两个基因源于一个基因复制事件，该事件独立于导致被子植物中具有线粒体或质体靶向特性的细胞器聚合酶的基因复制事件。然而，根据它们保守的外显子-内含子结构，它们是导致高等陆地植物RpoT基因的分子进化谱系的代表。
