ALKBH7-mediated demethylation regulates mitochondrial polycistronic RNA processing

Members of the mammalian AlkB family are known to mediate nucleic acid demethylation1,2. ALKBH7, a mammalian AlkB homologue, localizes in mitochondria and affects metabolism3, but its function and mechanism of action are unknown. Here we report an approach to site-specifically detect N1-methyladenosine (m1A), N3-methylcytidine (m3C), N1-methylguanosine (m1G) and N2,N2-dimethylguanosine (m22G) modifications simultaneously within all cellular RNAs, and discovered that human ALKBH7 demethylates m22G and m1A within mitochondrial Ile and Leu1 pre-tRNA regions, respectively, in nascent polycistronic mitochondrial RNA4-6. We further show that ALKBH7 regulates the processing and structural dynamics of polycistronic mitochondrial RNAs. Depletion of ALKBH7 leads to increased polycistronic mitochondrial RNA processing, reduced steady-state mitochondria-encoded tRNA levels and protein translation, and notably decreased mitochondrial activity. Thus, we identify ALKBH7 as an RNA demethylase that controls nascent mitochondrial RNA processing and mitochondrial activity.