CTP synthase (CTPS) catalyzes the formation of CTP in de novo pyrimidine biosynthesis pathway. Compartmentalization of CTPS into filamentous structure is evolutionarily conserved from E.coli, yeast, Drosophila, mice to humans. Previously, we demonstrated that histidine (His) mediated methylation promotes the formation of CTPS filament to suppress the enzymatic activity and preserve CTPS protein under Gln deprivation, which promotes cancer cell growth after stress alleviation. However, it remains unclear where and how these enigmatic structures are assembled. Here we used APEX2-mediated in vivo proximity labeling to identify proteins involve in the formation of human CTPS filaments.