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 seque nced. Clone hNR1-4 was isolated from a human hippocampus cDNA library and was presumably generated by alternative RNA splicing in the 3' ami no acid (aa) coding regions. The hNR1-4 cDNA demonstrated an 85.7% nuc leotide (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 w ith the corresponding rNR1 subunit. Clone hNR1N was isolated by polyme rase chain reaction (PCR)-mediated amplification of a 0.6-kb DNA fragm ent from human cerebellum cDNA. The nt sequence of this DNA fragment w as identical to previously isolated hNR1 cDNA clones, except for the p resence 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 pr esumably represents an exon that is subject to alternative splicing. T he nt and aa sequences of this exon are identical between human and ra t.