HUMAN GLUTAMATE PYRUVATE TRANSAMINASE (GPT) - LOCALIZATION TO 8Q24.3,CDNA AND GENOMIC SEQUENCES, AND POLYMORPHIC SITES

Two frequent protein variants of glutamate pyruvate transaminase (GPT) (E.C.2.6.1.2) have been used as genetic markers in humans for more th an two decades, although chromosomal mapping of the GPT locus in the 1 980s produced conflicting results. To resolve this conflict and develo p useful DNA markers for this gene, we isolated and characterized cDNA and genomic clones of GPT. We have definitively mapped human GPT to t he terminus of 8q using several methods. First, two cosmids shown to c ontain the GPT sequence were derived from a chromosome 8-specific libr ary. Second, by fluorescence in situ hybridization, we mapped the cosm id containing the human GPT gene to chromosome band 8q24.3. Third, we mapped the rat gpt cDNA to the syntenic region of rat chromosome 7. Fi nally, PCR primers specific to human GPT amplify sequences contained w ithin a ''half-YAC'' from the long arm of chromosome 8, that is, a YAC containing the 8q telomere. The human GPT genomic sequence spans 2.7 kb and consists of 11 exons, ranging in size from 79 to 243 bp. The ex onic sequence encodes a protein of 495 amino acids that is nearly iden tical to the previously reported protein sequence of human GPT-1. The two polymorphic GPT isozymes are the result of a nucleotide substituti on in codon 14, coding for a histidine in GPT-1 and an asparagine in G PT-2, which causes a gain or loss of an NlaIII restriction site. In ad dition, a cosmid containing the GPT sequence also contains a previousl y unmapped, polymorphic microsatellite sequence, D8S421. The cloned GP T gene and associated polymorphisms will be useful for linkage and phy sical mapping of disease loci that map to the terminus of 8q, includin g atypical vitelliform macular dystrophy (VMD1) and epidermolysis bull osa simplex, type Ogna (EBS1). In addition, this will be a useful syst em for characterizing the telomeric region of 8q. Finally, determinati on of the molecular basis of the GPT isozyme variants will permit PCR- based detection of this worldwide polymorphism. (C) 1997 Academic Pres s.