The relationship among the three cellular domains Archaea, Bacteria, and Eukarya has become a central problem in unraveling the tree of life. This relationship can now be studied as the completely sequenced genomes of representatives of these cellular domains become available. We performed a bioinformatic investigation of the Encephalitozoon cuniculi proteome. E. cuniculi has the smallest sequenced eukaryotic genome, 2.9 megabases coding for 1997 proteins. The proteins of E. cuniculi were compared with a previously characterized set of eukaryotic signature proteins (ESPs). ESPs are found in a eukaryotic cell, whether from an animal, a plant, a fungus, or a protozoan, but are not found in the Archaea and the Bacteria. We demonstrated that 85% of the ESPs have significant sequence similarity to proteins in E. cuniculi. Hence, E. cuniculi, a minimal eukaryotic cell that has removed all inessential proteins, still preserves most of the ESPs that make it a member of the Eukarya. The locations and functions of these ESPs point to the earliest history of eukaryotes.
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This research was supported in part by NSF Grandt DBI-0205512. Support for this work was provided by the Medical College of Ohio Foundation. We would also like to thank Ms. Lisa Johnston for her excellent secretarial assistance.
Reviewing Editor: Dr. Manyuan Long
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Fedorov, A., Hartman, H. What Does the Microsporidian E. cuniculi Tell Us About the Origin of the Eukaryotic Cell?. J Mol Evol 59, 695–702 (2004). https://doi.org/10.1007/s00239-003-0085-1