Expression of Trypanosoma cruzi surface antigen FL-160 is controlled by elements in the 3 ' untranslated, the 3 ' intergenic, and the coding regions

The FL-160 surface antigen gene family of T. cruzi consists of hundreds of members of 160 kDa glycoproteins expressed in trypomastigotes, but not in e pimastigotes. Steady-state levels of FL-160 mRNA were 80 to 100-fold higher in trypomastigotes than in epimastigotes, yet transcription rates were equ ivalent between the lifecycle stages. Luciferase reporter constructs demons trated that the 3' untranslated region (UTR) and intergenic region (IR) fol lowing the coding sequence of FL-160 was sufficient to generate 8-fold high er luciferase expression in trypomastigotes compared with epimastigotes. Tr ansfection of 3' UTR/IR deletion constructs revealed cis-acting elements wh ich conferred a trypomastigote-specific expression pattern similar to that of FL-160. Parasites treated with translation and transcription inhibitors, cyclohexamide and Actinomycin D, respectively, displayed a stage-specific pattern of FL-160 mRNA degradation. Epimastigotes, but not trypomastigotes, treated with the inhibitors accumulated a 1.4 Kb FL-160 cleavage product. The cleavage site mapped to a 31 base poly-purine tract in the FL-160 codin g region. The first 526 aa of FL-160, containing the 31 base poly-purine tr act and several smaller tracts, were fused to green fluorescent protein (GF P) and expressed from the T. cruzi tubulin locus. Stable transformants expr essed 4-fold more FL-160:GFP fusion mRNA and 12-fold more fusion protein in the trypomastigote stage than in the epimastigote stage suggesting post-tr anscriptional and translational control elements. These data reveal at leas t two distinct control mechanisms for trypomastigote-specific expression of FL-160 surface glycoproteins, one involving the 3' UTR/IR and one involvin g the coding region of FL-160. (C) 1999 Elsevier Science B.V. All rights re served.