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Proc Natl Acad Sci U S A. 2002 Feb 5;99(3):1420-5. Epub 2002 Jan 22.

The origin of the eukaryotic cell: a genomic investigation.

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Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

Erratum in

  • Proc Natl Acad Sci U S A 2002 Apr 2;99(7):4752.


We have collected a set of 347 proteins that are found in eukaryotic cells but have no significant homology to proteins in Archaea and Bacteria. We call these proteins eukaryotic signature proteins (ESPs). The dominant hypothesis for the formation of the eukaryotic cell is that it is a fusion of an archaeon with a bacterium. If this hypothesis is accepted then the three cellular domains, Eukarya, Archaea, and Bacteria, would collapse into two cellular domains. We have used the existence of this set of ESPs to test this hypothesis. The evidence of the ESPs implicates a third cell (chronocyte) in the formation of the eukaryotic cell. The chronocyte had a cytoskeleton that enabled it to engulf prokaryotic cells and a complex internal membrane system where lipids and proteins were synthesized. It also had a complex internal signaling system involving calcium ions, calmodulin, inositol phosphates, ubiquitin, cyclin, and GTP-binding proteins. The nucleus was formed when a number of archaea and bacteria were engulfed by a chronocyte. This formation of the nucleus would restore the three cellular domains as the Chronocyte was not a cell that belonged to the Archaea or to the Bacteria.

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