| Many members of the family Trypanosomatidae are parasites of humans and their domesticated livestock. Our research efforts have been focused on the study of regulated gene expression in Trypanosoma cruzi, which causes Chagas' disease in humans.;My work resulted in the establishment of a stable transformation system for T. cruzi, based on the integration of plasmid vectors into homologous sites on the genome. The generation of the stably transformed strain, clone ;The ability to perform gene replacements facilitated the analysis of the mechanisms regulating the differential expression of the ubiquitin gene complex. Enzyme assays and nuclear run-on analyses using the gene replacement strains demonstrated that although the genes and sequences comprising the ubiquitin gene complex of the 2.65 locus were expressed at different levels, they were transcribed at the same rate. This supports the concept that gene expression in T. cruzi, as in other trypanosomes, is regulated post-transcriptionally,;Gene replacements were also used to study the expression of the genes of the Ubiquitin gene complex of the 2.65 locus during the developmental cycle. A comparison of epimastigotes and amastigotes indicated that the CalA2 calmodulin gene was expressed at lower levels in amastigotes. However, the ubiquitin genes were found to be differentially regulated during differentiation. While the expression of the FUS1 ubiquitin-fusion gene was decreased in the intracellular amastigotes, the PUB12.5 polyubiquitin gene was constitutively expressed in both developmental forms. Since the 5;Many protein coding genes in trypanosomes are organized in multicopy gene families that are transcribed as long polycistronic pre-mRNAs, which are processed cotranscriptionally into mature monocistronic transcripts. All current evidence indicates that there is no regulation of transcription initiation in trypanosomes, the regulation of gene expression being primarily post-transcriptional. |
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