The NR1 subunit of the N-methyl-D-aspartate receptor can be efficiently expressed alone in the cell surface of mammalian cells and is required for the transport of the NR2A subunit

We have used a heterologous system of expression of N-methyl-D-aspartate (N MDA) receptors based on the use of vaccinia virus to analyse the maturation , transport, assembly and differential expression of the NR1 and NR2A subun its of the receptors. We have demonstrated that the NR1 subunit is efficien tly transported to the plasma membrane in cells expressing NR1 alone, simil arly to cells producing NR1 and NR2A together. In contrast, NR2A requires N R1 expression to be located at the cell surface. The stability of both rece ptor subunits expressed alone is similar to that obtained in cells producin g NR1 and NR2A. In pulse-chase experiments, the NR1 subunit displays a biph asic decay, with a fraction of the protein having a half-life of only 1 h a nd the remaining presenting a turnover longer than 24 h, similar to values obtained for the NR2A subunit. Our results also show a maturation process a ffecting the carbohydrate moiety in the NR1 subunit, such that immature NR1 has a much shorter half-life than the mature form or the NR2A subunit. Fin ally, we show that only a fraction of mature NR1 interacts with NR2A to for m multimeric functional complexes.