title: The nature of the last universal ancestor and the root of the tree of life, still open questions.
abstract: The nature of the last universal ancestor to all extent cellular organisms and the rooting of the universal tree of life are fundamental questions which can now be addressed by molecular evolutionists. Several scenarios have been proposed during the last years, based on the phylogenies of ribosomal RNA and of duplicated proteins, which suggest that the last universal ancestor was either an RNA progenote or an hyperthermophilic prokaryote. We discuss these hypotheses in the light of new data on the evolution of DNA metabolizing enzymes and of contradictions between different protein phylogenies. We conclude that the last universal ancestor was a member of the DNA world already containing several DNA polymerases and DNA topoisomerases. Furthermore, we criticize current data which suggest that the rooting of the universal tree of life is located in the eubacterial branch and we conclude that both rooting the universal tree and the nature of the last universal ancestor are still open questions.
authors.affiliation: Laboratoire des archaebactéries, URA 1354 CNRS, Université Paris-Sud, Orsay, France.
authors.forename: P
authors.initials: P
authors.lastname: Forterre
authors.forename: N
authors.initials: N
authors.lastname: Benachenhou-Lahfa
authors.forename: F
authors.initials: F
authors.lastname: Confalonieri
authors.forename: M
authors.initials: M
authors.lastname: Duguet
authors.forename: C
authors.initials: C
authors.lastname: Elie
authors.forename: B
authors.initials: B
authors.lastname: Labedan
mesh_terms: D001105:Archaea / Q000145:classification / Q000201:enzymology; D004264:DNA Topoisomerases, Type I / Q000145:classification; D004259:DNA-Directed DNA Polymerase / Q000145:classification; D005051:Eubacterium / Q000145:classification / Q000201:enzymology; D005057:Eukaryotic Cells / Q000201:enzymology; D008954:Models, Biological; D010802:Phylogeny; D011387:Prokaryotic Cells / Q000201:enzymology
chemical_list: D004259:DNA-Directed DNA Polymerase; D004264:DNA Topoisomerases, Type I