The study investigates the role of m6A_m, a reversible modification at the 5' cap of mRNA, in controlling mRNA stability. Using transcriptome-wide mapping, the researchers found that m6A_m-initiated transcripts are more stable than those starting with other nucleotides. This stability is attributed to resistance to the mRNA-decapping enzyme DCP2. Additionally, m6A_m is selectively demethylated by FTO, which reduces the stability of m6A_m-containing mRNAs. The findings suggest that the methylation status of m6A_m in the 5' cap is a dynamic and reversible epitranscriptomic modification that determines mRNA stability. The study also highlights the importance of m6A_m in mRNA stability, microRNA-mediated mRNA degradation, and translation efficiency.The study investigates the role of m6A_m, a reversible modification at the 5' cap of mRNA, in controlling mRNA stability. Using transcriptome-wide mapping, the researchers found that m6A_m-initiated transcripts are more stable than those starting with other nucleotides. This stability is attributed to resistance to the mRNA-decapping enzyme DCP2. Additionally, m6A_m is selectively demethylated by FTO, which reduces the stability of m6A_m-containing mRNAs. The findings suggest that the methylation status of m6A_m in the 5' cap is a dynamic and reversible epitranscriptomic modification that determines mRNA stability. The study also highlights the importance of m6A_m in mRNA stability, microRNA-mediated mRNA degradation, and translation efficiency.