EVOLUTIONARY SILENCING OF THE HUMAN ELASTASE-I GENE (ELA-1)

The human pancreatic elastase I gene is transcriptionally silent, desp ite the apparent integrity of the structural gene, The transcriptional regulatory sequences necessary and sufficient for transcription of th e active rat homologue are localized within 205 base pairs (bp) of the transcriptional start and comprise a pancreas-specific transcriptiona l enhancer of 134 bp immediately upstream of a 71 bp non-specific prom oter. The human gene has 58 nucleotide differences within this region, 13 of which are in the three functional elements (A, B and C) that co nstitute the enhancer, Through cell transfection analyses with a pancr eatic acinar tumor cell line, we show that the nucleotide differences in the human 5' flanking gene sequences have inactivated both the enha ncer and the promoter, The changes in the three elements of the human enhancer alone are sufficient to inactivate the enhancer; conversely, restores these to the rat configuration partially restores the activit y of the human enhancer, The two mutations in the A element and the fo ur mutations in the B element abolish the binding of the transcription factors previously shown to mediate the activity of these elements. R eplacing the active 71 bp rat promoter with the human promoter also pr events expression. Therefore, the evolutionary silencing of the human elastase I gene appears due to mutations that inactivate crucial enhan cer and promoter elements.