Active CTP synthase exists as a homotetrameric enzyme.
At low enzyme concentrations and in the absence of ATP and UTP, CTP synthase exists as inactive monomer.
As enzyme concentration increases, it polymerizes first to a dimer (such as the form shown to the left) and, in the presence of ATP and UTP, forms a tetramer.

The enzyme contains two major domains, responsible for the aminotransferase and synthase activity, respectively.
The amidotransferase domains are located away from the tetramer interfaces and are not affected by the oligomeric state.
The ATP-binding site and CTP-binding site in the synthase domain are located at the tetramer interface.
It is for this reason that ATP and UTP are required for tetramerization.
Active CTP synthase exists as a homotetrameric enzyme. At low enzyme concentrations and in the absence of ATP and UTP, CTP synthase exists as inactive monomer. As enzyme concentration increases, it polymerizes first to a dimer (such as the form shown to the left) and, in the presence of ATP and UTP, forms a tetramer.
The enzyme contains two major domains, responsible for the aminotransferase and synthase activity, respectively. The amidotransferase domains are located away from the tetramer interfaces and are not affected by the oligomeric state. The ATP-binding site and CTP-binding site in the synthase domain are located at the tetramer interface. It is for this reason that ATP and UTP are required for tetramerization.
CTP synthetase