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We recently characterized a large developmentally regulated gene family in Leishmania encoding the amastin surface proteins. While studying the regulation of these genes, we identified a region of 770 nucleotides (nt) within the 2055-nt 3′-untranslated region (3′-UTR) that regulates stage-specific gene expression at the level of translation. An intriguing feature of this 3′-UTR regulatory region is the presence of a ∼450-nt element that is highly conserved among several Leishmania mRNAs. Here we show, using a luciferase reporter system and polysome profiling experiments, that the 450-nt element stimulates translation initiation of the amastin mRNA in response to heat shock, which is the main environmental change that the parasite encounters upon its entry into the mammalian host. Deletional analyses depicted a second region of ∼100 nucleotides located at the 3′-end of several amastin transcripts …