MEPCE (methylphosphate capping enzyme) is a multifunctional protein that serves dual enzymatic and structural roles in RNA metabolism and transcriptional regulation. As an S-adenosyl-L-methionine-dependent methyltransferase, MEPCE adds methylphosphate caps to the 5'-ends of 7SK snRNA and U6 snRNAs, stabilizing these critical regulatory RNAs 1. Beyond its enzymatic function, MEPCE acts as a core component of the 7SK ribonucleoprotein (RNP) complex, where it collaborates with LARP7, HEXIM1/2, and 7SK snRNA to sequester positive transcription elongation factor b (P-TEFb) in an inactive state 2. This sequestration prevents RNA polymerase II phosphorylation and subsequent transcriptional elongation under homeostatic conditions 3. Notably, LARP7 interaction within the 7SK RNP complex occludes MEPCE's catalytic center, providing non-enzymatic regulation 2. MEPCE also participates in homologous recombination DNA repair by coordinating R-loop resolution at DNA double-strand breaks and facilitating RAD51 loading 4. Additionally, MEPCE contributes to human telomerase RNA biogenesis, working with LARP7 to process telomerase RNA precursors 5. Dysregulation of MEPCE has been implicated in cancer progression and neurodegenerative diseases, highlighting its clinical significance 36.