Trypanosoma cruzi: RNA structure and post-transcriptional control of tubulin gene expression.

Changes in tubulin expression are among the biochemical and morphological adaptations that occur during the life cycle of Trypanosomatids. To investigate the mechanism responsible for the differential accumulation of tubulin mRNAs in Trypanosoma cruzi, we determine the sequences of alpha- and beta-tubulin transcripts and analyzed their expression during the life cycle of the parasite. Two beta-tubulin mRNAs of 1.9 and 2.3 kb were found to differ mainly by an additional 369 nucleotides at the end of the 3' untranslated region (UTR). Although their transcription rates are similar in epimastigotes and amastigotes, alpha- and beta-tubulin transcripts are 3- to 6-fold more abundant in epimastigotes than in trypomastigotes and amastigotes. Accordingly, the half-lives of alpha- and beta-tubulin mRNAs are significantly higher in epimastigotes than in amastigotes. Transient transfection experiments indicated that positive regulatory elements occur in the 3' UTR plus downstream intergenic region of the alpha-tubulin gene and that both positive and negative elements occur in the equivalent regions of the beta-tubulin gene.