Cytosolic N6AMT1-dependent translation supports mitochondrial RNA processing to prevent double-stranded RNA accumulation

Mitochondrial biogenesis relies on both the nuclear and the mitochondrial genomes, and the mechanisms that support their coordinated expression are not fully understood. Improper mitochondrial DNA expression can lead to inborn error of metabolism, inflammation, and aging. Here, we investigate N6AMT1, a nucleo-cytosolic multi-substrate methyltransferase. We analyze genetic dependency, transcription, translation, and proteomic profiles of N6AMT1-depleted cells and report that N6AMT1 is necessary for the cytosolic translation of factors involved in mitochondrial RNA metabolism, including subunits of the mitochondrial RNase P. In the absence of N6AMT1, RNA processing and translation within mitochondria are impaired, while double-stranded RNA accumulates in mitochondrial RNA granules causing an interferon response. Our work highlights a cytosolic program required for proper mitochondrial biogenesis, with consequences on innate immunity.