m6Am-seq reveals the dynamic m6Am methylation in the human transcriptome.

N6,2'-O-dimethyladenosine (m6Am), a terminal modification adjacent to the mRNA cap, is a newly discovered reversible RNA modification. Yet, a specific and sensitive tool to directly map transcriptome-wide m6Am is lacking. Here, we report m6Am-seq, based on selective in vitro demethylation and RNA immunoprecipitation. m6Am-seq directly distinguishes m6Am and 5'-UTR N6-methyladenosine (m6A) and enables the identification of m6Am at single-base resolution and 5'-UTR m6A in the human transcriptome. Using m6Am-seq, we also find that m6Am and 5'-UTR m6A respond dynamically to stimuli, and identify key functional methylation sites that may facilitate cellular stress response. Collectively, m6Am-seq reveals the high-confidence m6Am and 5'-UTR m6A methylome and provides a robust tool for functional studies of the two epitranscriptomic marks.