In Chlamydomonas reinhardtii, chloroplast gene expression is tightly regulated post-transcriptionally by gene-specific trans-acting protein factors. Here we report the identification of an OctotricoPeptide Repeat (OPR) protein, MDH1, critical for the biogenesis of chloroplast ATP synthase CF0. At variance with most trans-acting factors characterised so far in C. reinhardtii that control the expression of a single gene, MDH1 targets two distinct transcripts: it is required for the accumulation and the translation of the atpH mRNA, encoding a subunit of the selective proton channel but it also enhances the translation of the atpI mRNA, which encodes the other subunit of the channel. MDH1 targets the 5'UTR of both atpH and atpI genes. Co-immuno-precipitation and small RNA sequencing revealed that MDH1 binds specifically a sequence highly conserved among Chlorophyceae and the Ulvale clade of Ulvophyceae at the 5'end of the tri-phosphorylated atpH mRNA. A very similar sequence, located about 60 nt upstream of the atpI initiation codon, was also conserved in some Chlorophyceae and Ulvale species and was found essential for atpI mRNA translation in C. reinhardtii. Such a dual targeted trans-acting factor, thus provides a mean to co-regulate the expression of the two proton hemi-channels.

在莱茵衣藻中，叶绿体基因表达在转录后受到基因特异性反式作用蛋白因子的严格调控。在这里我们报告鉴定的OctotricoPeptide重复（OPR）蛋白MDH1，对叶绿体ATP合酶CF0的生物发生至关重要。与迄今为止在莱茵衣藻中表征的控制单个基因表达的大多数反式作用因子有所不同，MDH1靶向两种截然不同的转录本：atpH mRNA的积累和翻译是必需的，其编码选择性的一个亚基质子通道，但它也增强了atpI mRNA的翻译，后者编码通道的另一个亚基。MDH1靶向atpH和atpI基因的5'UTR。免疫共沉淀和小分子RNA测序表明，MDH1在三磷酸化atpH mRNA的5'末端特异地结合了绿藻科和藻科的乌贼进化枝中高度保守的序列。在一些绿藻科和Ulvale物种中，atpI起始密码子上游约60 nt处的一个非常相似的序列也被保守，并且被发现对于莱茵衣藻中atpI mRNA翻译至关重要。因此，这种双重靶向的反式作用因子提供了共同调节两个质子半通道表达的手段。在某些绿藻科和Ulvale物种中也保守，并且被发现对于莱茵衣藻中atpI mRNA翻译至关重要。因此，这种双重靶向的反式作用因子提供了共同调节两个质子半通道表达的手段。在某些绿藻科和Ulvale物种中也保守，并且被发现对于莱茵衣藻中atpI mRNA翻译至关重要。因此，这种双重靶向的反式作用因子提供了共同调节两个质子半通道表达的手段。