Journal of Molecular Evolution

, Volume 59, Issue 5, pp 606–619

The Origin of Eukaryotes Is Suggested as the Symbiosis of Pyrococcus into γ-Proteobacteria by Phylogenetic Tree Based on Gene Content

  • Tokumasa Horiike
  • Kazuo Hamada
  • Daisuke Miyata
  • Takao Shinozawa

DOI: 10.1007/s00239-004-2652-5

Cite this article as:
Horiike, T., Hamada, K., Miyata, D. et al. J Mol Evol (2004) 59: 606. doi:10.1007/s00239-004-2652-5


Attempts were made to define the relationship among the three domains (eukaryotes, archaea, and eubacteria) using phylogenetic tree analyses of 16S rRNA sequences as well as of other protein sequences. Since the results are inconsistent, it is implied that the eukaryotic genome has a chimeric structure. In our previous studies, the origin of eukaryotes to be the symbiosis of archaea into eubacteria using the whole open reading frames (ORF) of many genomes was suggested. In these studies, the species participating in the symbiosis were not clarified, and the effect of gene duplication after speciation (in-paralog) was not addressed. To avoid the influence of the in-paralog, we developed a new method to calculate orthologous ORFs. Furthermore, we separated eukaryotic in-paralogs into three groups by sequence similarity to archaea, eubacteria (other than α-proteobacteria), and α-proteobacteria and treated them as individual organisms. The relationship between the three ORF groups and the functional classification was clarified by this analysis. The introduction of this new method into the phylogenetic tree analysis of 66 organisms (4 eukaryotes, 13 archaea, and 49 eubacteria) based on gene content suggests the symbiosis of pyrococcus into γ-proteobacteria as the origin of eukaryotes.


Origin Eukaryote Nucleus symbiosis Phylogenetic tree Gene content 

Copyright information

© Springer Science + Business Media Inc. 2004

Authors and Affiliations

  • Tokumasa Horiike
    • 1
  • Kazuo Hamada
    • 2
  • Daisuke Miyata
    • 3
  • Takao Shinozawa
    • 4
  1. 1.Center of Information Biology and DNA Data Bank of Japan, National Institute of GeneticsResearch Organization of Information and SystemsMishimaJapan
  2. 2.Advanced Research Institute for Science and EngineeringWaseda UniversityHonjyoJapan
  3. 3.Department of Environment Systems, Faculty of Geo-Environmental ScienceRissho UniversityKumagayaJapan
  4. 4.Graduate School of Science and EngineeringWaseda University, Waseda Research Park, IOC Honjo-WasedaHonjoJapan

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