Structural organization of the human gamma-glutamyl hydrolase gene.

Gamma-glutamyl hydrolase (GH) plays an important role in the metabolism of folic acid and the pharmacology of antifolates such as methotrexate. We have previously cloned and characterized the human GH cDNA. In this report, the complete organization and structure of the human GH gene was determined. The human GH gene spans 24 kb in the human genome, with nine exons sized from 51 to 371 bp. All of exon-intron splice junctions follow the GT-AG rule. The sequence upstream of exon 1 consists of a promoter-like, GC-rich region and a number of putative cis active elements including Sp1, AP1, and MZF1 sites. A TATA sequence in the 5' region of human GH gene was not observed, similar to housekeeping genes known to be tissue-specific and differentially expressed. S1 nuclease protection analysis with human liver, prostate, brain, and mammary gland revealed a major transcription start point at nucleotide -125 relative to the ATG start codon and several minor transcription start points. Analysis of GH cDNA isolated from human liver indicated a nucleotide change, T-->C, in the leader sequence of GH, which suggested a polymorphism. Studies of cDNA from different human tissue sources provided evidence that there is a single spliced cDNA species in human.