THE NOVEL CORE PROMOTER ELEMENT GAAC IN THE HGL5 GENE OF ENTAMOEBA-HISTOLYTICA IS ABLE TO DIRECT A TRANSCRIPTION START SITE INDEPENDENT OF TATA OR INITIATOR REGIONS

Entamoeba histolytica, an enteric protozoa, is the third leading paras itic cause of death worldwide. Investigation of the transcriptional ma chinery of this eukaryotic pathogen has revealed an unusual core promo ter structure that consists of nonconsensus TATA and initiator regions and a novel third conserved core promoter sequence, the GAAC element. Mutation of this region in the hgl5 promoter decreases reporter gene expression and alters the transcription start site. Using positional a nalysis of this element, we have now demonstrated that it is able to d irect a new transcription start site, 2-7 bases downstream of itself, independent of TATA and Inr regions. The GAAC region was also shown to control the rate of transcription via nuclear run on analysis and an amebic nuclear protein was demonstrated to specifically interact with this sequence. This is the first description in the eukaryotic literat ure of a third conserved core promoter element, distinct from TATA or initiator regions, that is able to direct a transcription start site. We have formulated two models for the role of the GAAC region: (i) the GAAC-binding protein is a part of the TFIID complex and (ii) the GAAC -binding protein functions to ''tether'' TATA-binding protein to the T ATA box.