Archaea and the Origin(s) of DNA Replication Proteins

The deepest phylogenetic division in the universal tree (vertical line in Figure 1) is that separating bacteria from the clade comprising archaea and eukaryotes. The prokaryote–eukaryote split (horizontal line in Figure 1), originally delineated on the basis of differences between (eu)bacterial and eukaryotic cellular ultrastructure, is a phenetic dichotomy (see Doolittle, 1996, and references therein). How useful this dichotomy still is remains an active question: its answer will come from a full appreciation of molecular and cellular differences between