A PURINE-RICH SEQUENCE IN THE HUMAN BM-40 GENE PROMOTER REGION IS A PREREQUISITE FOR MAXIMUM TRANSCRIPTION

BM-40 (osteonectin, SPARC [secreted protein, acidic, rich in cysteine] ) is a highly conserved, matrix-associated protein that is found in ba sement membranes, bones and remodeling tissues throughout vertebrate e volution. We are reporting the characterization of the 5' end of the h uman BM-40 gene. Sequence comparison of the 5' region revealed signifi cant homologies with the bovine and murine genes, including a purine-r ich stretch composed of two boxes, GGA-box 1 and 2, separated by a pyr imidine-rich spacer element. Transfection analyses of the human BM-40 promoter provide strong evidence that this region comprises several di stinct regulatory domains, to which different functions can be assigne d. GGA-box 1 is thereby absolutely required and sufficient by itself f or maximal BM-40 transcriptional activity, whereas the spacer element has a down-regulatory effect. Comparative transfection analyses in hum an cell lines, positive or negative for BM-40 transcripts, indicate th at the GGA-box sequences in the human promoter, in contrast to the bov ine promoter, do not significantly contribute to cell-type specific ex pression in human cells.