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UBC Theses and Dissertations

Ubiquitin gene expression during differentiation of Leishmania major Ma, Tosca Chiu Wah


Leishmania major (L. major) is an intra-macrophage protozoan parasite which differentiates from a promastigote to an amastigote upon transmission from its insect vector at 25°C to its mammalian host at 37°C. This temperature shift occurs in the same range as that used to elicit the heat shock response in prokaryotes and higher eukaryotes in which the induction of genes encoding heat shock proteins is seen. Ubiquitin is a heat inducible protein and one of the most conserved eukaryotic proteins known. Genomic libraries made from major DNA were initially screened with the ubiquitin gene from yeast. DNA sequence analyses of positive clones revealed at least 5 ubiquitin coding elements arranged head to tail without intervening sequences. The predicted protein sequence showed that ubiquitin in Leishmania differs from that of yeast and barley at 5 out of 76 amino acid positions and from that of human at only 2 positions. Further characterization revealed another ubiquitin encoding locus believed to carry only one ubiquitin encoding element. Comparisons of ubiquitin mRNA levels from L. major grown at 26°C, 37°C, and 42°C suggest that ubiquitin gene expression in these particular parasites is constitutive and that prolonged exposure at a non-lethal temperature results in a reduction of ubiquitin-specific mRNA. However, a direct correlation between parasite differentiation and ubiquitin gene expression was not defined as it could not be determined whether the described experimental conditions actually established differentiated states of L. major.

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