title: Direct evidence for secondary loss of mitochondria in Entamoeba histolytica.
abstract: Archezoan protists are though to represent lineages that diverged from other eukaryotes before acquisition of the mitochondrion and other organelles. The parasite Entamoeba histolytica was originally included in this group. Ribosomal RNA based phylogenies, however, place E. histolytica on a comparatively recent branch of the eukaryotic tree, implying that its ancestors had these structures. In this study, direct evidence for secondary loss of mitochondrial function was obtained by isolating two E. histolytica genes encoding proteins that in other eukaryotes are localized in the mitochondrion: the enzyme pyridine nucleotide transhydrogenase and the chaperonin cpn60. Phylogenetic analysis of the E. histolytica homolog of cpn60 confirmed that it is specifically related to the mitochondrial lineage. The data suggest that a mitochondrial relic may persist in this organism. Similar studies are needed in archezoan protists to ascertain which, if any, eukaryotic lineages primitively lack mitochondria.
authors.affiliation: Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-0425, USA.
authors.forename: C G
authors.initials: CG
authors.lastname: Clark
authors.forename: A J
authors.initials: AJ
authors.lastname: Roger
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D016384:Consensus Sequence; D016786:Eimeria tenella / Q000235:genetics; D004748:Entamoeba histolytica / Q000145:classification* / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D009250:NADP Transhydrogenases / Q000737:chemistry / Q000235:genetics*; D010802:Phylogeny; D012335:RNA, Ribosomal / Q000235:genetics; D012247:Rhodospirillum rubrum / Q000201:enzymology; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity
chemical_list: D012335:RNA, Ribosomal; D009250:NADP Transhydrogenases