Structural organization of the human folypoly-gamma-glutamate synthetase gene: evidence for a single genomic locus.

The cytotoxicity, and probably the selectivity, of folate antimetabolites depend upon the expression of the enzyme folylpoly-gamma-glutamate synthetase in tumor cells. Evidence for the existence of multiple forms of this enzyme and the need to define the control mechanisms determinant of expression levels in normal and neoplastic cells has focused attention on the gene(s) encoding these forms. The organization of the genomic locus for the human folylpoly-gamma-glutamate synthetase (FPGS) gene has been determined. The complete 2256 nucleotides of cDNA for the 5'-untranslated region, mitochondrial leader sequence, coding region, and 3'-untranslated region were distributed on 15 exons stretching over 11.2 kb of genomic DNA. All of the restriction fragments found in diploid human genomic DNA could be accounted for by fragments contained on the isolated genomic clones. Likewise, Southern analysis of the transfected human genomic DNA that complemented the FPGS- phenotype of a hamster cell line indicated that the same gene had been integrated in all of three independently derived transfectants. We conclude that the genomic locus that we now report appears to be the only gene encoding FPGS-related sequences in the human complement.