RNMT (RNA guanine-7 methyltransferase) is the catalytic subunit of the mRNA-capping methyltransferase RNMT:RAMAC complex that catalyzes 7-methylguanosine (m7G) cap formation on mRNAs 1. The enzyme methylates the N7 position of guanosine at the 5' end of mRNA transcripts and binds RNA containing 5'-terminal GpppC 2. This m7G cap protects transcripts from degradation and recruits factors mediating splicing, nuclear export, and translation initiation 1. RNMT function is dynamically regulated during development and differentiation. During neural differentiation, RNMT repression is required to suppress pluripotency genes while allowing CMTR1-mediated histone and ribosomal protein expression 2. RNMT also coordinates mRNA cap methylation with ribosomal RNA production through c-Myc regulation 3. Additionally, RNMT interacts directly with cap-binding protein eIF4E, facilitating coupling of cap maturation with translation initiation 4. Pathologically, RNMT dysregulation contributes to cancer progression. In osteosarcoma, the CYFIP1/RNMT/AURKAIP1 axis promotes cuproptosis through m7G-dependent mRNA modification 5. Pan-cancer analysis reveals RNMT expression correlates with prognosis and immune infiltration across multiple tumor types, particularly lung squamous cell carcinoma 6. Coronaviruses hijack RNMT to enhance viral protein translation and replication 7.