Structure of the murine Pit1 phosphate transporter/retrovirus receptor gene and functional characterization of its promoter region

The Pitl phosphate transporter (formerly also called G1vr-l) probably plays an important role in regulated phosphate handling in bone-forming cells. I n this study, we describe the structure of the mouse Pitl gene, as well as some functional characteristics of its promoter legion in murine bone cells . Screening of a genomic library led to the isolation of two overlapping lamb da clones containing 7 kb of 5' flanking region, as well as the 10 exons of the mouse Pitl gene corresponding to the published cDNA. The translation s tart site is located within exon I and the stop codon within exon X. The overall structure of the mouse gene is very similar to that of its huma n homolog, except for the presence of an additional 5' untranslated exon in human. The structure of the 5' untranslated region of the mouse gene was t hus further investigated using rapid amplification of cDNA ends in murine A TDC5, MC3T3-E1 and Swiss 3T3 cells. The results indicate that, compared to the published cDNA, the mouse Pitl gene contains in fact one additional 5' exon, which we named exon IA. Reporter gene assays demonstrate the presence of a functional TATA box containing promoter upstream of exon IA. This description of the murine Pitl gene and of its promoter region paves t he way to more detailed analyses concerning the regulation of Pitl transcri ption in mouse cells. Furthermore, a comparison of mouse and human promoter s will hopefully allow a better understanding of general mechanisms regulat ing Pitl expression in different species. (C) 2000 Elsevier Science B.V. Al l rights reserved.