title: A nuclear gene of eubacterial origin in Euglena gracilis reflects cryptic endosymbioses during protist evolution.
abstract: Genes for glycolytic and Calvin-cycle glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher eukaryotes derive from ancient gene duplications which occurred in eubacterial genomes; both were transferred to the nucleus during the course of endosymbiosis. We have cloned cDNAs encoding chloroplast and cytosolic GAPDH from the early-branching photosynthetic protist Euglena gracilis and have determined the structure of its nuclear gene for cytosolic GAPDH. The gene contains four introns which possess unusual secondary structures, do not obey the GT-AG rule, and are flanked by 2- to 3-bp direct repeats. A gene phylogeny for these sequences in the context of eubacterial homologues indicates that euglenozoa, like higher eukaryotes, have obtained their GAPDH genes from eubacteria via endosymbiotic (organelle-to-nucleus) gene transfer. The data further suggest that the early-branching protists Giardia lamblia and Entamoeba histolytica--which lack mitochondria--and portions of the trypanosome lineage have acquired GAPDH genes from eubacterial donors which did not ultimately give rise to contemporary membrane-bound organelles. Evidence that "cryptic" (possibly ephemeral) endosymbioses during evolution may have entailed successful gene transfer is preserved in protist nuclear gene sequences.
authors.affiliation: Institut für Genetik, Technische Universität Braunschweig, Federal Republic of Germany.
authors.forename: K
authors.initials: K
authors.lastname: Henze
authors.forename: A
authors.initials: A
authors.lastname: Badr
authors.forename: M
authors.initials: M
authors.lastname: Wettern
authors.forename: R
authors.initials: R
authors.lastname: Cerff
authors.forename: W
authors.initials: W
authors.lastname: Martin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D005075:Biological Evolution; D002467:Cell Nucleus / Q000378:metabolism*; D016384:Consensus Sequence; D005051:Eubacterium / Q000145:classification* / Q000235:genetics*; D005056:Euglena gracilis / Q000235:genetics*; D056890:Eukaryota / Q000145:classification* / Q000235:genetics*; D005658:Fungi / Q000145:classification / Q000235:genetics; D005798:Genes, Bacterial; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics*; D007438:Introns; D008969:Molecular Sequence Data; D005810:Multigene Family; D009690:Nucleic Acid Conformation; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013559:Symbiosis
chemical_list: D012329:RNA, Bacterial; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases