The nascent m6A methylome in human cells

Here, we profiled N6-methyladenosine (m6A) deposition on nascent RNAs in human cells by a new method MINT-Seq, which revealed that many classes of RTE RNAs, particularly intronic LINE-1s (L1s), are strongly methylated. These m6A-marked intronic L1s (MILs) are evolutionarily young, sense-oriented to hosting genes and nucleate a dozen RNA binding proteins (RBPs) that are putative novel m6A readers, including a nuclear matrix protein SAFB. Notably, m6A positively controls the expression of both autonomous L1s and co-transcribed L1 relics, promoting L1 retrotransposition. We showed that MILs preferentially reside in long genes, where they act as transcriptional 'roadblock' to impede the hosting gene expression, revealing a novel host-weakening strategy by the L1s. In counteraction, the host uses the SAFB reader complex to bind m6A-L1s to reduce their levels, and to safeguard hosting gene transcription. Overall design: The lanscape of m6A methylation on nascent RNAs in human cells