CLONING AND SEQUENCE-ANALYSIS OF CDNAS ENCODING HUMAN HIPPOCAMPUS N-METHYL-D-ASPARTATE RECEPTOR SUBUNITS - EVIDENCE FOR ALTERNATIVE RNA SPLICING

Several cDNA clones encoding human N-methyl-D-aspartate receptor (hNR1 ) subunit polypeptides were isolated from a human hippocampus library. Degenerate oligodeoxyribonucleotide (oligo) primers based on the publ ished rat NR1 (rNR1) amino acid (aa) sequence [K. Moriyoshi et al. Nat ure 354 (1991) 31-37] amplified a 0.7-kb fragment from a human hippoca mpus cDNA library, via the polymerase chain reaction (PCR). This fragm ent was used as a probe for subsequent hybridization screening. DNA se quence analysis of 28 plaque-purified clones indicated three distinct classes, designated hNR1-1, hNR1-2 and hNR1-3, presumably generated by alternative RNA splicing. One of these clones, hNR1-1(5A), was isolat ed as a full-length cDNA. The hNR1-2 and hNR1-3 cDNAs represented 66.8 and 98.9%, respectively, of the total aa coding information predicted for the polypeptides. The hNR1 cDNAs demonstrated an 84-90.8% nucleot ide (nt) identity with the corresponding rodent cDNAs. The nt sequence s of hNR1-1, hNR1-2 and hNR1-3 would encode 885-, 901- and 938-aa prot eins, respectively, that have 99.1-99.8% identity with the correspondi ng rodent NR1 (roNR1) subunits. The changes between the predicted aa s equences of hNR1 and the corresponding roNR1 subunits are confined to the extracellular N-terminal regions. We have also identified two poss ible allelic variations of the hNR1-3 cDNA that result in aa substitut ions in the extracellular N- and C-terminal regions. One of these natu rally occurring aa variations is situated within a potential glutamate -binding site.