THE PUTATIVE PROMOTER FOR A METACYCLIC VSG GENE IN AFRICAN TRYPANOSOMES

During their metacyclic developmental stage, African trypanosomes are coated with one of 12-15 variant surface glycoproteins (VSGs) that def ine different metacyclic variant antigen types (MVATs). The MVAT VSG g enes are located near telomeres of large chromosomes and are expressed without rearrangement in the metacyclic stage. We have cloned and exa mined the telomere-linked MVAT5 VSG gene and its upstream expression s ite associated gene (ESAG I) which are separated by 4.5 kb. Within thi s 4.5-kb intergenic region is an 87-bp sequence that serves as a stron g promoter for a luciferase reporter gene in transient transfection as says. This 87-bp sequence is similar, but not identical, to the promot er for another MVAT VSG gene. UV irradiation experiments were used to detect RNA synthesis from this MVAT5 promoter in bloodstream trypanoso mes expressing an unrelated VSG. We propose that this sequence is a sp ecific promoter for the MVAT5 VSG mRNA that occurs in about 10% of the trypanosome population during the metacyclic stage of the parasites' life cycle.