ALKBH7-mediated demethylation regulates mitochondrial polycistronic RNA processing

Members of the mammalian AlkB family are known to mediate nucleic acid demethylation 1 , 2 . ALKBH7, a mammalian AlkB homologue, localizes in mitochondria and affects metabolism 3 , but its function and mechanism of action are unknown. Here we report an approach to site-specifically detect N 1 -methyladenosine (m 1 A), N 3 -methylcytidine (m 3 C), N 1 -methylguanosine (m 1 G) and N 2 , N 2 -dimethylguanosine (m 2 2 G) modifications simultaneously within all cellular RNAs, and discovered that human ALKBH7 demethylates m 2 2 G and m 1 A within mitochondrial Ile and Leu1 pre-tRNA regions, respectively, in nascent polycistronic mitochondrial RNA 4 – 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.