The mitochondrial genome encodes 13 components of the oxidative phosphorylation system, and altered mitochondrial transcription drives various human pathologies. A polyadenylated, non-coding RNA molecule known as 7S RNA is transcribed from a region immediately downstream of the light strand promoter in mammalian cells, and its levels change rapidly in response to physiological conditions. Here, we report that 7S RNA has a regulatory function, as it controls levels of mitochondrial transcription both in vitro and in cultured human cells. Using cryo-EM, we show that POLRMT dimerization is induced by interactions with 7S RNA. The resulting POLRMT dimer interface sequesters domains necessary for promoter recognition and unwinding, thereby preventing transcription initiation. We propose that the non-coding 7S RNA molecule is a component of a negative feedback loop that regulates mitochondrial transcription in mammalian cells.

线粒体基因组编码氧化磷酸化系统的 13 种成分，线粒体转录的改变驱动了各种人类疾病。一种称为 7S RNA 的多聚腺苷酸化非编码 RNA 分子从哺乳动物细胞中轻链启动子的下游区域转录，其水平响应生理条件迅速变化。在这里，我们报告 7S RNA 具有调节功能，因为它在体外控制线粒体转录水平在培养的人体细胞中。使用冷冻电镜，我们表明 POLRMT 二聚化是由与 7S RNA 的相互作用诱导的。由此产生的 POLRMT 二聚体界面隔离了启动子识别和展开所必需的结构域，从而阻止了转录起始。我们提出非编码 7S RNA 分子是调节哺乳动物细胞线粒体转录的负反馈环的一个组成部分。