STRUCTURAL ORGANIZATION OF THE HUMAN FOLYLPOLY-GAMMA-GLUTAMATE SYNTHETASE GENE - EVIDENCE FOR A SINGLE GENOMIC LOCUS

The cytotoxity, and probably the selectivity, of folate antimetabolite s depend upon the expression of the enzyme folylpoly-gamma-glutamate s ynthetase in tumor cells, Evidence for the existence of multiple forms of this enzyme and the need to define the control mechanisms determin ant of expression levels in normal and neoplastic cells has focused at tention on the gene(s) encoding these forms, The organization of the g enomic locus for the human folylpoly-gamma-glutamate synthetase (FPGS) gene has been determined, The complete 2256 nucleotides of cDNA for t he 5'-untranslated region, mitochondrial leader sequence, coding regio n, and 3'-untranslated region were distributed on 15 exons stretching over 11.2 lib of genomic DNA. All of the restriction fragments found i n diploid human genomic DNA could he accounted for by fragments contai ned 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 integrat ed in all of three independently derived transfectants, We conclude th at the genomic locus that we now report appears to be the only gene en coding FPGS-related sequences in the human complement.