Institute of Molecular Biology, University of Oregon, Eugene, OR 97403, USA.
Department of Life Sciences, Institute of Biology, Humboldt University Berlin, 10115 Berlin, Germany.
Nucleic Acids Res. 2018 Nov 2;46(19):10448-10459. doi: 10.1093/nar/gky737.
Pentatricopeptide repeat (PPR) proteins are a large family of helical repeat proteins that bind RNA in mitochondria and chloroplasts. Sites of PPR action have been inferred primarily from genetic data, which have led to the view that most PPR proteins act at a very small number of sites in vivo. Here, we report new functions for three chloroplast PPR proteins that had already been studied in depth. Maize PPR5, previously shown to promote trnG splicing, is also required for rpl16 splicing. Maize PPR10, previously shown to bind the atpI-atpH and psaJ-rpl33 intercistronic regions, also stabilizes a 3'-end downstream from psaI. Arabidopsis PGR3, shown previously to bind upstream of petL, also binds the rpl14-rps8 intercistronic region where it stabilizes a 3'-end and stimulates rps8 translation. These functions of PGR3 are conserved in maize. The discovery of new functions for three proteins that were already among the best characterized members of the PPR family implies that functional repertoires of PPR proteins are more complex than have been appreciated. The diversity of sequences bound by PPR10 and PGR3 in vivo highlights challenges of predicting binding sites of native PPR proteins based on the amino acid code for nucleotide recognition by PPR motifs.
五肽重复（PPR）蛋白是一类富含螺旋重复结构的蛋白，能够与线粒体和叶绿体中的 RNA 结合。PPR 蛋白的作用靶点主要是通过遗传数据推断得到的，这导致人们普遍认为大多数 PPR 蛋白在体内仅作用于极少数的靶点。在这里，我们报道了三个已被深入研究的叶绿体 PPR 蛋白的新功能。先前已证明玉米 PPR5 蛋白可促进 trnG 剪接，它也是 rpl16 剪接所必需的。先前已证明玉米 PPR10 蛋白可结合 atpI-atpH 和 psaJ-rpl33 顺式作用元件区，还可稳定 psaI 下游的 3'端。先前已证明拟南芥 PGR3 蛋白可结合 petL 的上游区，它还可结合 rpl14-rps8 顺式作用元件区，稳定该区域的 3'端并刺激 rps8 翻译。在玉米中也发现了 PGR3 的这些功能。三个 PPR 蛋白已被广泛研究，它们的新功能的发现意味着 PPR 蛋白的功能谱比以前认为的更为复杂。PPR10 和 PGR3 在体内结合的序列多样性凸显了基于 PPR 基序对核苷酸识别的氨基酸代码预测天然 PPR 蛋白结合位点的挑战。
