Mapping N6 -Methyladenosine (m6 A) in RNA: Established Methods, Remaining Challenges, and Emerging Approaches.

N6 -Methyladenosine (m6 A) is the most abundant internal modification in eukaryotic mRNA. Specific m6 A reader and eraser proteins link this modification to many aspects of mRNA metabolism and regulate its levels in a dynamic way. Precise localization and quantification in varying biological samples is, therefore, relevant to understand the functional role of m6 A and mechanisms governing its regulation. In this Minireview, we summarize established and emerging concepts for m6 A mapping. Starting with the seminal m6 A-sequencing techniques based on immunoprecipitation, we will highlight technical improvements by photo-cross-linking and remaining challenges. As an alternative, antibody-free approaches will be presented. These include wild-type or engineered m6 A-sensitive enzymes and chemical biology approaches combining substrate analogues, chemical derivatization, and enzymatic steps to trace m6 A. Finally, single-molecule sequencing as a new avenue for direct detection of mRNA modifications will be discussed.