STRUCTURE AND REGULATION OF A POLYMORPHIC GENE ENCODING FOLATE RECEPTOR-TYPE GAMMA GAMMA'/

The human folate receptor (hFR) type gamma and gamma' are constitutive ly secreted proteins that are expressed primarily in hematopoietic tis sues and are potential serum markers for certain hematopoietic maligna ncies. hFR-gamma' is a variant of hFR-gamma with a two base deletion i n its cDNA resulting in a truncated polypeptide. The gene encoding hFR -gamma' was isolated from a placental genomic library. The gene has fi ve exons, four introns and a 5' flanking sequence which contains multi ple putative regulatory elements. From RNase protection assay and RACE analysis, the major site of transcriptional initiation was identified at -56 nt. Systematically deleted fragments in the 5' region of the g enomic DNA of FR-gamma' were ligated into the PGL(3) Basic plasmid and the reporter luciferase activity was assayed in cell lysates from tra nsiently transfected NIH3T3 cells, From those results, putative positi ve and negative regulatory regions in the 5' flanking sequences were n oted, and a TATA-less proximal promoter was located between -206 and - 22 nt. Gel mobility shift and supershift analyses as well as mutagenes is experiments revealed that Spl and ets binding elements in the proxi mal promoter region confer transcriptional activity. From partial sequ encing of genomic DNA, genomic Southern blots, RACE analysis and RNase protection assays, it appears that hFR-gamma shares the gene organiza tion of hFR-gamma'. The results of the analysis of genomic DNA in sple en tissues from several individuals, were consistent with the interpre tation that hFR-gamma and hFR-gamma' are encoded by a polymorphic gene .