Organization of the 5′-End of the Porcine γ-Glutamyl Transpeptidase Gene and Identification of Three Different mRNAs in the Kidney

Three different mRNAs coding for the porcine γ-glutamyl transpeptidase (GGT) in the kidney were identified by 5′-RACE-PCR. These differ in their 5′-noncoding region. Genomic Southern blot analysis has demonstrated the existence of a single GGT gene in the porcine genome. Thus, the existence of multiple mRNAs can only be explained by the use of different promoters or alternative splicing. Four GGT-specific genomic clones containing the complete 5′-end of the gene were isolated and characterized, revealing six exons common to all three mRNAs. Four of these exons were located in the coding region comprising the codons for amino acids 1 to 138. Two exons and an intervening sequence were identified upstream from these six common exons representing the unique 5′-ends of the three mRNAs. The coding exons show a significant sequence homology to mouse, rat, and human GGT cDNA, whereas exons 1 and 3 display no homology.