TRANSCRIPTION INITIATION IS CONTROLLED BY 3 CORE PROMOTER ELEMENTS INTHE HGL5 GENE OF THE PROTOZOAN PARASITE ENTAMOEBA-HISTOLYTICA

Entamoeba histolytica is a single cell eukaryote that is the etiologic agent of amoebic colitis. Core promoter elements of B. histolytica pr otein encoding genes include a TATA-like sequence (GTATTTAAAG/C) at -3 0, a novel clement designated GAAC (GAACT) that has a variable locatio n between TATA and the site of transcription initiation, and a putativ e initiator (Inr) element (AAAAATTCA) overlying the site of transcript ion initiation, The presence of three separate conserved sequences in a eukaryotic core promoter is unprecedented and prompted examination o f their roles in regulating transcription initiation, Alterations of a ll three regions in the hgl5 gene decreased reporter gene activity wit h the greatest effect seen by mutation of the GAAC element, positional analysis of the TATA box demonstrated that transcription initiated co nsistently 30-31 a bases downstream of the TATA region, Mutation of ei ther the TATA or GAAC elements I resulted in the appearance of new tra nscription start sites upstream of +1 in the promoter of the hgl5 gene , Mutation of the Inr element resulted in no change in the site of tra nscription initiation; however, in the presence of a mutated TATA and GAAC regions, the Inr element controlled the site of transcription ini tiation, We conclude that all three elements play a role in determinin g the site of transcription initiation, The variable position of the G AAC element relative to the site of transcription initiation, and the multiple transcription initiations that resulted from its mutation, in dicate that the GAAC element has an important and apparently novel rol e in transcriptional control in E. histolytica.