Laboratoire de Physiologie Membranaire et Moléculaire du Chloroplaste -UMR7141, IBPC, CNRS-Sorbonne Université, 13, rue Pierre et Marie Curie, 75005, Paris, France.
Plant J. 2019 Jun;98(6):1033-1047. doi: 10.1111/tpj.14300. Epub 2019 Apr 4.
In Chlamydomonas reinhardtii, chloroplast gene expression is tightly regulated post-transcriptionally by gene-specific trans-acting protein factors. Here, we report the molecular identification of an OctotricoPeptide Repeat (OPR) protein, MDA1, which governs the maturation and accumulation of the atpA transcript, encoding subunit α of the chloroplast ATP synthase. As does TDA1, another OPR protein required for the translation of the atpA mRNA, MDA1 targets the atpA 5'-untranslated region (UTR). Unexpectedly, it binds within a region of approximately 100 nt in the middle of the atpA 5'-UTR, at variance with the stabilization factors characterized so far, which bind to the 5'-end of their target mRNA to protect it from 5' → 3' exonucleases. It binds the same region as TDA1, with which it forms a high-molecular-weight complex that also comprises the atpA mRNA. This complex dissociates upon translation, promoting degradation of the atpA mRNA. We suggest that atpA transcripts, once translated, enter the degradation pathway because they cannot reassemble with MDA1 and TDA1, which preferentially bind to de novo transcribed mRNAs.
在莱茵衣藻中，叶绿体基因的表达在转录后受到基因特异性的反式作用蛋白因子的严格调控。在这里，我们报告了一个 OctotricoPeptide Repeat（OPR）蛋白 MDA1 的分子鉴定，它控制着编码叶绿体 ATP 合酶亚基α的 atpA 转录本的成熟和积累。与另一种翻译 atpA mRNA 所必需的 OPR 蛋白 TDA1 一样，MDA1 靶向 atpA 5'非翻译区（UTR）。出乎意料的是，它结合在 atpA 5'-UTR 的大约 100 个核苷酸的中间区域，与迄今为止表征的稳定因子不同，后者结合到其靶 mRNA 的 5'端，以防止其受到 5'→3'外切核酸酶的降解。它与 TDA1 结合在相同的区域，与 TDA1 形成一个高分子量的复合物，该复合物还包含 atpA mRNA。该复合物在翻译后解离，促进 atpA mRNA 的降解。我们认为，一旦 atpA 转录本被翻译，它们就会进入降解途径，因为它们不能与 MDA1 和 TDA1 重新结合，MDA1 和 TDA1 优先结合新转录的 mRNA。
