5'-regulatory elements of the human HPRT gene

The 5'-flanking sequences influencing expression of the human HPRT gene have been examined by introducing various HPRT minigenes into HPRT-deficient hamster fibroblasts by Ca(PO4)2-mediated gene transfer followed by quantitation of stable HPRT+ transformants. The promoter element has been localized within a region 210 bp upstream from the ATG codon. In addition, a negative regulator element (NRE) has been identified upstream from the promoter. Deletion of this NRE causes a ten-fold increase in the frequency of HPRT+ transformants. A transient expression assay involving microinjection of the minigenes into the HPRT- cells and monitoring of tritium incorporation into nucleic acid following uptake of labelled hypoxanthine suggested that this effect may be the result of increased transcriptional activity