Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA.
RNA. 2012 Jun;18(6):1197-209. doi: 10.1261/rna.032623.112. Epub 2012 Apr 10.
A maize gene designated thylakoid assembly 8 (tha8) emerged from a screen for nuclear mutations that cause defects in the biogenesis of chloroplast thylakoid membranes. The tha8 gene encodes an unusual member of the pentatricopeptide repeat (PPR) family, a family of helical repeat proteins that participate in various aspects of organellar RNA metabolism. THA8 localizes to chloroplasts, where it associates specifically with the ycf3-2 and trnA group II introns. The splicing of ycf3-2 is eliminated in tha8 mutants, and trnA splicing is strongly compromised. Reverse-genetic analysis of the tha8 ortholog in Arabidopsis thaliana showed that these molecular functions are conserved, although null alleles are embryo lethal in Arabidopsis and seedling lethal in maize. Whereas most PPR proteins have more than 10 PPR motifs, THA8 belongs to a subfamily of plant PPR proteins with only four PPR motifs and little else. THA8 is the first member of this subfamily with a defined molecular function, and illustrates that even small PPR proteins have the potential to mediate specific intermolecular interactions in vivo.
一个被命名为类囊体装配 8（tha8）的玉米基因是从一个筛选核突变的筛选中出现的，这些突变导致叶绿体类囊体膜生物发生缺陷。tha8 基因编码五肽重复（PPR）家族的一个不寻常成员，该家族是一种螺旋重复蛋白，参与细胞器 RNA 代谢的各个方面。THA8 定位于叶绿体，在那里它与 ycf3-2 和 trnA 组 II 内含子特异性结合。在 tha8 突变体中，ycf3-2 的剪接被消除，trnA 的剪接受到严重影响。拟南芥中 tha8 同源物的反向遗传分析表明，这些分子功能是保守的，尽管在拟南芥中，tha8 的缺失等位基因是胚胎致死的，而在玉米中是幼苗致死的。虽然大多数 PPR 蛋白具有超过 10 个 PPR 基序，但 THA8 属于植物 PPR 蛋白的一个亚家族，只有四个 PPR 基序，几乎没有其他基序。THA8 是这个亚家族中第一个具有明确分子功能的成员，它表明即使是小的 PPR 蛋白也有可能在体内介导特定的分子间相互作用。
