Origin of tRNA Genes in Trypanosoma and Leishmania and Comparison of Eukaryote Phylogenies Obtained from Mitochondrial rRNA and Protein Sequences

Abstract

<p> Two studies are presented in this thesis. First part is about the origin of tRNA genes in Trypanosoma and Leishmania. These organisms have special mitochondrial DNA, termed kinetoplast DNA (kDNA), which is unique in its structure and function. kDNA is a massive network which is composed of thousands of connected DNA circles. Unlike most other mitochondrial genomes, there is no gene encoding tRNAs in their kDNAs. So all the tRNAs used in mitochondria must be encoded on nuclear genes and transported from the cytoplasm into the mitochondria. So our question of interest is where the tRNA genes in their nucleus come from. We carry out phylogenetic analysis of these genes and the corresponding ones in bacteria, mitochondria and eukaryotic nuclei. There is no evidence indicating gene transfer from mitochondria to nucleus on the basis of this analysis. These results are consistent with the simplest hypothesis, i.e. that all tRNA genes of Trypanosoma and Leishmania have the same origin as nuclear genes of other eukaryotes.</p> <p> The second part is about the comparison of eukaryote phylogenies obtained from mitochondrial rRNA and protein sequences. We carried out phylogenetic analysis for the species which have complete mitochondrial genomes by using both concatenated mitochondrial rRNA and protein sequences. We got phylogenies for three groups, fungi/metazoan, plant/algae and stramenopile/alveolate group. The analysis is useful for the further study of position of the genetic code changes and the mechanisms involved.</p>