Cloning and sequence analysis of additional splice variants encoding human N-methyl-D-aspartate receptor (hNR1) subunits.

Two cDNA clones representing previously unidentified human N-methyl-D-aspartate receptor (hNR1) subunit polypeptides were isolated and sequenced. Clone hNR1-4 was isolated from a human hippocampus cDNA library and was presumably generated by alternative RNA splicing in the 3' amino acid (aa) coding regions. The hNR1-4 cDNA demonstrated an 85.7% nucleotide (nt) identity to the corresponding rat NR1 (rNR1) cDNA. The nt sequence of hNR1-4 would encode a protein that has a 99.8% identity with the corresponding rNR1 subunit. Clone hNR1N was isolated by polymerase chain reaction (PCR)-mediated amplification of a 0.6-kb DNA fragment from human cerebellum cDNA. The nt sequence of this DNA fragment was identical to previously isolated hNR1 cDNA clones, except for the presence of a 63-bp DNA insertion that would encode an additional 21 aa. This DNA insertion occurs in the 5' aa coding regions of hNR1 and presumably represents an exon that is subject to alternative splicing. The nt and aa sequences of this exon are identical between human and rat.