library_construction_protocol: mESCs were spiked with 2% of human cells (HeLa), then poly(A) RNA was extracted using the Magnetic mRNA Isolation Kit (NEB) with two rounds of enrichment. Immunoprecipitation of m6A methylated RNA (MeRIP) was done using the EpiMark® N6-Methyladenosine Enrichment Kit with 4µg spiked poly(A) RNA. MeRIP libraries were constructed from 0.5-1ng of input or IP RNA and prepared using the SMARTR-seq RNA library prep v2 kit (TakaraBio), per manufacturer's recommendations.