| Research Abstract |
Study on the mechanism of nucleus symbiosis by homology-hit analysis
Based on phylogenetic tree analysis, it has been considered that the appearance of eukaryotic cells by branching from archae involved those branching from eubacteia. This analysis was mainly carried out using 16S-rRNA genes. However, the above results are confusing when other genes are used for analysis.
Therefore, we have developed a new method, named as the homology-hit analysis, for the analysis of huge numbers of genes. By this method, after the selection of orthologous genes among many organisms, analysis of homologies among orthologous genes at many thresholds is possible. We have applied this new analysis to yeast, as a representative eukaryotic cell, 6 archaea and 9 eubacteria. Homologies of genes for each functional category in yeast were evaluated in comparison With those of archaea or eubacteria. As a result, it was concluded that the origins of genes related to cell nuclei and-cytoplasm, including the cell m
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embrane, are archaea and eubacteria, respectively.
To determine the species involved in symbiosis, phylogenetic tree analysis, evaluating the relationships among organisms by the number of orthologous genes, was carried out for 4 eukaryotes, 13 archaea and 49 eubacteria. For this, new method for the removal of duplicated genes was developed. Finally the origin of eukaryote was clarified as the symbiosis of pyrococcus into γ-proteobacteria.
To consider the background of symbiosis, we have focused on the protection of the cell against oxygen by the molecular chaperones, including catalases. Cloning of the catalase gene from an alkali- and halo-tolerant bacterium and expression of the catalase in E.coli were performed, followed by an improvement in heat stability by gene-technology. A proposal for a systematic computer-oriented nomenclature and constitution of a database for molecular chaperones were also made. In addition, work related to codon usage in eukaryotes, the distribution of repetitive sequences in E.coli, and others were carried out. Less
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