title: Life-cycle and growth-phase-dependent regulation of the ubiquitin genes of Trypanosoma cruzi.
abstract: BACKGROUND
  Trypanosoma cruzi, the causative agent of Chagas disease, exhibits a complex life cycle that is accompanied by the stage-specific gene expression. At the molecular level, very little is known about gene regulation in trypanosomes. Complex gene organizations coupled with polycistronic transcription units make the analysis of regulated gene expression difficult in trypanosomes. The ubiquitin genes of T. cruzi are a good example of this complexity. They are organized as a single cluster containing five ubiquitin fusion (FUS) and five polyubiquitin (PUB) genes that are polycistronically transcribed but expressed differently in response to developmental and environmental changes.
  
  
  METHODS
  Gene replacements were used to study FUS and PUB gene expression at different stages of growth and at different points in the life cycle of T. cruzi.
  
  
  RESULTS
  Based on the levels of reporter gene expression, it was determined that FUS1 expression was downregulated as the parasites approached stationary phase, whereas PUB12.5 polyubiquitin gene expression increased. Conversely, FUS1 expression increases when epimastigotes and amastigotes differentiate into trypomastigotes, whereas the expression of PUB12.5 decreases when epimastigotes differentiate into amastigotes and trypomastigotes.
  
  
  CONCLUSIONS
  Although the level of CAT activity in logarithmic growing epimastigotes is six- to seven-fold higher when the gene was expressed from the FUS1 locus than when expressed from the PUB12.5 locus, the rate of transcription from the two loci was the same implying that post-transcriptional mechanisms play a dominant role in the regulation of gene expression.
authors.affiliation: Departamento de Biomedicina Molecular, Centro de Investigación y de Estudios Avanzados del IPN, México, D.F., México. rmanning@cinvestav.mx
authors.forename: Rebeca
authors.initials: R
authors.lastname: Manning-Cela
authors.forename: Sobha
authors.initials: S
authors.lastname: Jaishankar
authors.forename: John
authors.initials: J
authors.lastname: Swindle
mesh_terms: D000818:Animals; D014355:Chagas Disease / Q000235:genetics / Q000469:parasitology; D005786:Gene Expression Regulation / Q000502:physiology*; D005796:Genes / Q000235:genetics; D006801:Humans; D015800:Protozoan Proteins / Q000096:biosynthesis* / Q000235:genetics; D014349:Trypanosoma cruzi / Q000235:genetics / Q000254:growth & development*; D025801:Ubiquitin / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D015800:Protozoan Proteins; D025801:Ubiquitin