Chloroplast genes encoding photosynthesis-associated proteins are predominantly transcribed by the plastid-encoded RNA polymerase (PEP). PEP is a multi-subunit complex composed of plastid-encoded subunits similar to bacterial RNA polymerases (RNAPs) stably bound to a set of nuclear-encoded PEP-associated proteins (PAPs). PAPs are essential to PEP activity and chloroplast biogenesis, but their roles are poorly defined. Here, we present cryoelectron microscopy (cryo-EM) structures of native 21-subunit PEP and a PEP transcription elongation complex from white mustard (). We identify that PAPs encase the core polymerase, forming extensive interactions that likely promote complex assembly and stability. During elongation, PAPs interact with DNA downstream of the transcription bubble and with the nascent mRNA. The models reveal details of the superoxide dismutase, lysine methyltransferase, thioredoxin, and amino acid ligase enzymes that are subunits of PEP. Collectively, these data provide a foundation for the mechanistic understanding of chloroplast transcription and its role in plant growth and adaptation.

中文翻译：

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植物质体编码的RNA聚合酶的结构


编码光合作用相关蛋白的叶绿体基因主要由质体编码的RNA聚合酶（PEP）转录。 PEP 是一种多亚基复合物，由类似于细菌 RNA 聚合酶 (RNAP) 的质体编码亚基组成，稳定地结合到一组核编码的 PEP 相关蛋白 (PAP) 上。 PAP 对 PEP 活性和叶绿体生物发生至关重要，但其作用尚不清楚。在这里，我们展示了天然 21 亚基 PEP 和来自白芥末的 PEP 转录延伸复合物的冷冻电子显微镜 (cryo-EM) 结构 ()。我们发现 PAP 包裹核心聚合酶，形成广泛的相互作用，可能促进复杂的组装和稳定性。在延伸过程中，PAP 与转录泡下游的 DNA 以及新生的 mRNA 相互作用。该模型揭示了超氧化物歧化酶、赖氨酸甲基转移酶、硫氧还蛋白和氨基酸连接酶（PEP 亚基）的详细信息。总的来说，这些数据为叶绿体转录及其在植物生长和适应中的作用的机制理解提供了基础。