Challenges to m6A mapping of viral RNA. (A) Identification of viral m6A profiles requires the ability to map m6A residues and long-read sequencing to identify isoforms of modified viral RNA molecules. (B) Single-nucleotide mapping of viral m6A is needed for increased resolution that is difficult to obtain with immunoprecipitation (IP)-based m6A mapping strategies. (C) Quantifying the stoichiometry of m6A in a pool of expressed transcripts requires a fully quantitative method of measurement not possible using IP-based m6A mapping methods. (D) Measuring m6A in populations of viral RNA in different phases of viral replication is hampered by the limitation of enriching enough RNA to meet the input requirements of many m6A mapping methods.
