The mitochondrial genome transcribes 13 mRNAs coding for well-known proteins essential for oxidative phosphorylation. We demonstrate here that cytochrome b (CYTB), the only mitochondrial-DNA-encoded transcript among complex III, also encodes an unrecognized 187-amino-acid-long protein, CYTB-187AA, using the standard genetic code of cytosolic ribosomes rather than the mitochondrial genetic code. After validating the existence of this mtDNA-encoded protein arising from cytosolic translation (mPACT) using mass spectrometry and antibodies, we show that CYTB-187AA is mainly localized in the mitochondrial matrix and promotes the pluripotent state in primed-to-naive transition by interacting with solute carrier family 25 member 3 (SLC25A3) to modulate ATP production. We further generated a transgenic knockin mouse model of CYTB-187AA silencing and found that reduction of CYTB-187AA impairs females’ fertility by decreasing the number of ovarian follicles. For the first time, we uncovered the novel mPACT pattern of a mitochondrial mRNA and demonstrated the physiological function of this 14^th protein encoded by mtDNA.

线粒体基因组转录 13 个 mRNA，编码氧化磷酸化所必需的众所周知的蛋白质。我们在此证明，细胞色素b ( CYTB ) 是复合物 III 中唯一由线粒体 DNA 编码的转录本，它也使用胞质核糖体的标准遗传密码而不是线粒体遗传密码。使用质谱和抗体验证了这种由胞质翻译 (mPACT) 产生的 mtDNA 编码蛋白的存在后，我们发现 CYTB-187AA 主要定位于线粒体基质中，并通过相互作用促进从启动到初始转变的多能状态与溶质载体家族 25 成员 3 (SLC25A3) 一起调节 ATP 产生。我们进一步建立了 CYTB-187AA 沉默的转基因敲入小鼠模型，发现 CYTB-187AA 的减少会通过减少卵泡数量来损害雌性的生育能力。我们首次发现了线粒体 mRNA 的新型 mPACT 模式，并证明了 mtDNA 编码的第 14^个蛋白质的生理功能。