Methylphosphate Capping Enzyme (MEPCE)

Gel filtration confirmed that P-TEFb, HEXIM1, and SART3 cofractionated with MEPCE, and RNA blot analysis showed that 7SK (RN7SK) and U6 (RNU6) small nuclear RNAs were also present in the complex. In the presence of radiolabeled S-adenosyl methionine, recombinant MEPCE methylated recombinant 7SK in vitro. MEPCE required 5-prime phosphates of 7SK, demonstrating that MEPCE is a 7SK methylphosphate capping enzyme. Silencing of MEPCE by small interfering RNA decreased the steady-state level of cellular 7SK, suggesting that MEPCE stabilizes 7SK by adding a methylphosphate cap at its 5-prime end.deduced 689-amino acid protein has a central RNA methylase domain and a C-terminal Bin3 domain. Database analysis revealed homologs of MEPCE in both higher and lower eukaryotes.