Life's Third Domain (Archaea): An Established Fact or an Endangered Paradigm? A New Proposal for Classification of Organisms Based on Protein Sequences and Cell Structure

The three-domain proposal of Woese et al. (Proc. Natl. Acad. Sci. USA 87, 4576 (1990)) divides all living organisms into three primary groups or domains named Archaea (or archaebacteria), Bacteria (or eubacteria), and Eucarya (or eukaryotes), with Eucarya being relatives (or descendants) of Archaea. Although this proposal is currently widely accepted, sequence features and phylogenies derived from many highly conserved proteins are inconsistent …