Adenosine-uridine-rich element is one of the required cis-elements for epimastigote form stage-specific gene expression of the congolense epimastigote specific protein.

It is known that gene expression in kinetoplastida is regulated post-transcriptionally. Several previous studies have shown that stage-specific gene expression in trypanosomes is regulated by cis-elements located in the 3' untranslated region (UTR) of each mRNA and also by RNA binding proteins. Our previous study revealed that gene expression of congolense epimastigote specific protein (cesp) was regulated by cis-elements located in the 3'UTR. In the present study, we identified the adenosine and uridine rich region in the cesp 3'UTR. Using transgenic trypanosome cell lines with different egfp expression cassettes, we showed that this adenosine and uridine rich region is one of the regulatory elements for epimastigote form (EMF) stage-specific gene expression via the regulatory cis-element of the eukaryotic AU rich element (ARE). Therefore this required element within the cesp 3'UTR was designated as T. congolense ARE. This required cis-element might selectively stabilize mRNA in the EMF stage and destabilize mRNA in other stages. By RNA electro mobility shift assay, unknown stage-specific RNA binding proteins (RBPs) whose sequences specifically interacted with the required cis-element were found. These results indicate that EMF stage specific cis-element and RBP complexes might specifically stabilize cesp mRNA in EMF.