The cytoplasmic C-terminal domains of NR2 subunits have been proposed to modulate the assembly and trafficking of NMDA receptors.However,questions remain concerning which domains in the C-terminus of NR2 subunits control the assembly of receptor complexes and how the assembled complexes are selectively trafficked through the various cellular compartments such as endoplasmic reticulum (ER) to the cell surface.In the present study,we found that the three amino-acid tail after the TM4 region of NR2 subunits is necessary for surface expression of functional NMDA receptors,while tnmcations with only two amino-acids following the TM4 region (NR2-2) completely eliminated surface expression of the NMDA receptor on co-expression with NR1-1 a in HEK293 cells.