This enzyme is involved in the de novo synthesis of CTP, a precursor of DNA, RNA and phospholipids. Catalyzes the ATP-dependent amination of UTP to CTP with either L-glutamine or ammonia as a source of nitrogen. This enzyme and its product, CTP, play a crucial role in the proliferation of activated lymphocytes and therefore in immunity. ATP + H2O + L-glutamine + UTP = ADP + CTP + 2 H(+) + L-glutamate + phosphate Activated by GTP and inhibited by CTP. Pyrimidine metabolism; CTP biosynthesis via de novo pathway; CTP from UDP: step 2/2. Mainly cytosolic but when active detected in long filamentous structures (By similarity). Co-localizes with TNK2 in the cytosolic filaments (By similarity). Belongs to the CTP synthase family.