DOCSLIB.ORG

Archaebacterial Genomes: Eubacterial Form and Eukaryotic Content

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Archaebacterial Genomes: Eubacterial Form and Eukaryotic Content Archaebacterial genomes: eubacterial form and eukaryotic content Patrick J Keeling, Robert LCharlebois and W Ford Doolittle Dalhousie University, Halifax and University of Ottawa, Ottawa, Canada Since the recognition of the uniqueness and coherence of the archaebacteria (sometimes called Archaea), our perception of their role in early evolution has been modified repeatedly. The deluge of sequence data and rapidly improving molecular systematic methods have combined with a better understanding of archaebacterial molecular biology to describe a group that in some ways appears to be very similar to the eubacteria, though in others is more like the eukaryotes. The structure and contents of archaebacterial genomes are examined here, with an eye to their meaning in terms of the evolution of cell structure and function. Current Opinion in Genetics and Development 1994, 4:816-822 Introduction this review we will focus on more recent discoveries and try to assimilate these observations with phylogeny. As molecular phylogenetics advances, it provides evolu- tionary biologists with a f&rework on which to assem- ble a coherent picture of the history of life. Two un- Archaebacterial genome design expected discoveries that emerged from sequence com- parisons have had particularly far-reaching effects on our At present, seven archaebacterial genomes have been view of early evolution; both concern the archaebacteria. physically mapped. In each case, the genome is com- The first, on the basis of ribosomal RNA (rRNA) se- posed of a single circular chromosome that falls within quence information, and now extensively supported by a the size range observed in the eubacteria [5-11,12”,13*] variety of other data, was the finding that the prokaryotes (Table 1). In several instances, extrachromosomal ele- are actually composed of two distinct groups, eubacteria ments have also been identified [14]; in some halophiles, and archaebacteria, as distant horn one another as either plasmid and megaplasmid (up to 700 kb) DNA makes are f%om the eukaryotes [l]. The second, equally excit- up a substantial portion of the genome [15]. Halophile ing discovery is that the eubacteria branched first from plasmids and chromosomes bear scores of transposable the universal tree, so that the archaebacteria and eukary- elements, which give rise to high frequencies of ge- otes seem to be sister groups [2]. The significance of this netic instability as revealed by spontaneous mutations and second conclusion (which, although increasingly popu- local genetic rearrangements detectable through South- lar, does need confirmation from additional data sets) is ern analysis [16]. This phenomenon can be observed on that it allows us to propose specific arguments about the the time scale of laboratory experiments, but compara- nature of both the prokaryotic ancestor of the eukary- tive mapping indicates that in evolutionary time, chro- otes and the last common ancestor of all extant life on mosomal order is remarkably conserved in halobacteria the basis of characters shared between pairs of taxa. (P Lopez-Garcia, A St Jean, R Amils, R Charlebois, un- published data; N Hackett, personal communication). As our understanding of the archaebacteria on the Forces must exist that can effectively oppose the pow- molecular level develops, it is becoming clear that they erful destabilizing pressures present in the halobacterial share a number of features in overall genome design and genome. gene organization with the eubacteria. These traits can then be said most parsimoniously to be ancestral to all Archaebacterial and eubacterial genomes are similar in life. Many other characters, particularly those involved size and structure, both being small, compact, and cir- with gene expression, are shared between the archae- cular. If the rooting of the universal tree by Iwabe [2] is bacteria and eukaryotes; these can be either primitive correct, it is reasonable to suppose that this design is an- or derived, but in both cases help us to understand the cestral to all extant life, although we know too few of the order of evolutionary events at or near the origin of the details of genome construction to be certain that the trait eukaryotes. Detailed reviews of archaebacterial molecu- could not have evolved twice independently. To describe lar biology are available in two recent books [3,4], so in the nature of the primitive genome more accurately, we Abbreviation snoRNA-small nucleolar RNA. 816 0 Current Biology Ltd ISSN 0959-437X Archaebacterial genomes Keeling, Charlebois and Doolittle 817 order S12-S7-EF-G-EF-Tu for both M. uunnielii and Table 1. Archaebacterial genome sizes as determined by mapping. E. coli [28]). In one case, the M. vannielii Ll operon, the similarity can be extended to the regulation of ex- Species Cenome size Method References pression, as it has been shown that the Ll protein in M. vannielii represses translation of its own mRNA by bind- Mefhanococcus voltae 1900 PFC I71 ing to a site that resembles its binding site on the 23s tialobacrerium halobium 2400 PFC 1101 rRNA [25**]. The same autoregulation is seen in E. coli, Halobacterium sp. CR6 2472 Cloning [12-l differing only in the position of the binding site on the Haloferax volcanii 4140 Cloning 161 mRNA. Haloferax mediterranei 3840 PFG l8,13*1 Thermococcus celer 1890 PFG 151 Enough data may not be available to say that gene or- Sulfolobus acidocaldarius 2760 PFG I91 der is conserved over even longer distances in eubacterial and archaebacterial chromosomes, but enough is known Summary of archaebacterial genomes that have been mapped. Each to begin to assemble some intriguing correlations. The of these gendmes is within the range of genome size documented in spectinomycin operon is immediately downstream of the eubacteria and all finished maps are circular. PFG, pulsed-field gel the SlO operon in both E. coli and M. vannielii [17], electrophoresis. and the streptomycin operon is followed by the SlO operon in Themotogu maritima and by the SlO protein (the first reading tie in the SlO operon) in three d& need more comparative data and a better understanding ferent archaebacteria [28], as well as in the cyanobac- of archaebacterial genomes Corn a functional standpoint; terium Spinrlina platensis [29]. The current best guess for instance, the mechanisms of replication initiation, is that in the ancestor of archaebacteria wd eubac- termination, and chromosomal segregation need to be teria, these three operons followed one another in the examined. order streptomycin-SlO-spectinomycin, with the genes in each being similar to those found commonly in con- Archaebacterial gene organization temporary operons. In general, the structure of archaebacterial genes closely The transition to eukaryotes resembles that of eubacteria [15,17]. They are organized into co-transcribed units, or operons, that are expressed A particularly close afinity between archaebacteria and as long non-capped mRNAs with only short bacterial- eukaryotes has been long suspected, but for the most part like poly(A) tails [18]. Protein-coding genes of the ar- on vague grounds - resistance to certain drugs, lack chaebacteria are not disrupted by introns of any type, of peptidoglycan, or the occurrence of tRNA introns other than some spliced at the protein level [19,20], and [30]. Recent work, however, has elucidated a ham&l to date no intron resembling the nuclear spliceosomal of molecular similarities that argue unambiguously for a type has been identified. Introns have been found in shared inheritance with the eukaryotes, three of which 16S, 23s. and tRNA genes; these are of a novel type, are reviewed here. dependent upon a defined secondary structure at the intron/exon boundary and an unidentified enzymatic One of the strongest similarities is in transcription mech- activity [21]. Some of these introns have been found to anisms, now known to dif&r fundamentally &om the contain open reading frames related to homing endonu- homologous eubacterial process. Evidence for this simi- cleases first characterized in group I self-splicing introns larity has been accumulating for a number of years, be- of mitochondria and eubacteriophages [22*]. ginning with the observation that archaebacterial RNA polymerases are multisubunit complexes, unlike the sim- The degree of similarity between archaebacterial and ple three or four subunit eubacterial enzyme [31,32], eubacterial operons or operon clusters is best exemplified and that the consensus archaebacterial promoter bears by a number of archaebacterial operons that contain the a closer resemblance to the eukaryotic TATA box than same genes in the same order as their eubacterial homo- to eubacterial promoter sequences [33]. The depth of logs (reviewed in [23]; see Fig. 1). These include the this similarity was further revealed when the existence of RNA polymerase operon and ribosomal protein gene an archaebacterial homolog of the eukaryotic transcrip- clusters, which are homologous to the Escherichiu colt’ tion &ctor TFIIB was discovered by a database search Lll and LlO clusters (four of four genes in the same [34,35*], and by wo reports of a gene that encodes order in two archaebacteria and E. coli [24,25”]). the a protein closely resembling both TFIIS and a subunit spectinomycin operon (for which Methunococcusvunnielii of eukaryotic RNA polymerases I and II [36’,37*]. and Sulfolobus ucidoculduriusshow eleven and nine, respec- Moreover, work by two independent investigators has tively, of the eleven E. coli genes in the same order, now shown that archaebacterial genomes also encode although the archaebacteria each have three ‘extras’, TFIID, or the TATA-binding protein [38”,39”], and which are homologs of eukaryotic ribosomal protein that TFIID recognizes archaebacterial promoters and genes [24,26]), the SlO operon (seven genes in a stretch directs the binding of TFIIB [39”]. Unlike their eubac- of seven in the same order in halobacteria and E. coli terial counterparts, eukaryotic RNA polymerases alone [27]), and the streptomycin operon (four genes in the cannot recognize promoters; instead, the assembly of the 818 Genomes and evolution ‘Lll , LlO Clusters E.
Load more

Recommended publications
  • The Myth of Junk DNA
    The Myth of Junk DNA JoATN h A N W ells s eattle Discovery Institute Press 2011 Description According to a number of leading proponents of Darwin’s theory, “junk DNA”—the non-protein coding portion of DNA—provides decisive evidence for Darwinian evolution and against intelligent design, since an intelligent designer would presumably not have filled our genome with so much garbage. But in this provocative book, biologist Jonathan Wells exposes the claim that most of the genome is little more than junk as an anti-scientific myth that ignores the evidence, impedes research, and is based more on theological speculation than good science. Copyright Notice Copyright © 2011 by Jonathan Wells. All Rights Reserved. Publisher’s Note This book is part of a series published by the Center for Science & Culture at Discovery Institute in Seattle. Previous books include The Deniable Darwin by David Berlinski, In the Beginning and Other Essays on Intelligent Design by Granville Sewell, God and Evolution: Protestants, Catholics, and Jews Explore Darwin’s Challenge to Faith, edited by Jay Richards, and Darwin’s Conservatives: The Misguided Questby John G. West. Library Cataloging Data The Myth of Junk DNA by Jonathan Wells (1942– ) Illustrations by Ray Braun 174 pages, 6 x 9 x 0.4 inches & 0.6 lb, 229 x 152 x 10 mm. & 0.26 kg Library of Congress Control Number: 2011925471 BISAC: SCI029000 SCIENCE / Life Sciences / Genetics & Genomics BISAC: SCI027000 SCIENCE / Life Sciences / Evolution ISBN-13: 978-1-9365990-0-4 (paperback) Publisher Information Discovery Institute Press, 208 Columbia Street, Seattle, WA 98104 Internet: http://www.discoveryinstitutepress.com/ Published in the United States of America on acid-free paper.
    [Show full text]
  • Reproduction, Symbiosis, and the Eukaryotic Cell
    Reproduction, symbiosis, and the eukaryotic cell Peter Godfrey-Smith1 Philosophy Program, City University of New York Graduate Center, City University of New York, New York, NY 10016; and History and Philosophy of Science Unit, University of Sydney, Sydney, NSW 2006, Australia Edited by W. Ford Doolittle, Dalhousie University, Halifax, NS, Canada, and approved March 27, 2015 (received for review December 30, 2014) This paper develops a conceptual framework for addressing because the pattern of inheritance and the distribution of fitness questions about reproduction, individuality, and the units of differences may cancel, yielding no net change across genera- selection in symbiotic associations, with special attention to the tions (10, 11), but it still is a lucid summary of how Darwinian origin of the eukaryotic cell. Three kinds of reproduction are evolution works. As Lewontin emphasized, many different kinds distinguished, and a possible evolutionary sequence giving rise to of objects—including genes, organelles, cells, demes, and other a mitochondrion-containing eukaryotic cell from an endosymbiotic social groups—can satisfy Darwin’s scheme. All can form pop- partnership is analyzed as a series of transitions between each of ulations of units with variation, heritability, and fitness differ- the three forms of reproduction. The sequence of changes seen in ences. However, this use of the concepts of heritability and fitness this “egalitarian” evolutionary transition is compared with those takes for granted the idea of reproduction and especially the ex- that apply in “fraternal” transitions, such as the evolution of multi- istence of parent–offspring lineages between members of a pop- cellularity in animals. ulation.
    [Show full text]
  • An Interview with Ford Doolittle
    INTERVIEW The Philosophical Approach: An Interview with Ford Doolittle Jane Gitschier* Departments of Medicine and Pediatrics and Institute for Human Genetics, University of California San Francisco, San Francisco, California, United States of America * [email protected] For years, the whiteboard in my office brimmed with ideas for potential interviewees. Names were erased when an interview was completed, and new names added when a particular topic piqued my interest. Some were arranged in a kind of Venn diagram by their fields, and one such cluster—concerning the origins of early life forms—included three deep thinkers: Lynn Margulis, whose 1967 paper articulated the endosymbiotic origin of mitochondria and chloro- plasts; Carl Woese, whose attempts to classify prokaryotes based on ribosomal RNA cataloging led to his championing the new kingdom of Archaea in 1977; and Ford Doolittle (Fig 1), who provided evidence for Margulis’s hypothesis using Woese’s methods. Though Woese and Mar- gulis are now deceased, Doolittle, I can attest, is very much alive and, dare I say, “kicking!” Over time, Doolittle has cogitated on a variety of intriguing evolutionary questions, including the origin of introns, the role of lateral gene transfer in speciation, and the meaning of “func- tion.” He is always worth listening to. Doolittle grew up in Champaign-Urbana, Illinois, the son of an art professor and now hold- ing a BFA in photography himself. As a high-school friend of the late Sol Spiegelman’s son, he worked with Spiegelman in the summers. Following undergraduate studies at Harvard and graduate work with Charles Yanofsky at Stanford, he returned to Spiegelman’s lab for postdoc- toral work and then joined Norman Pace when Spiegelman moved to New York.
    [Show full text]
  • Lovelock on Gaia
    18.12 concepts 769 AM 12/12/03 5:40 pm Page 769 concepts The living Earth Gaia evidence, these earlier ideas remained anec- James Lovelock dotal. In 1925 Alfred Lotka conjectured that Organisms and their environment magine a science-based civilization far it would be easier to model the evolution of evolve as a single, self-regulating distant in the Galaxy that had built an organisms and their material environment system. Iinterferometer of such resolving power coupled as a single entity than either of them that it could analyse the chemical composi- separately. Gaia had its origins in these earlier tion of our atmosphere. Simply from this thoughts, from the evidence gathered by the track temperature change, not regulate it. analysis, they could confidently conclude biogeochemists Alfred Redfield and Evelyn But the restraining function connecting that Earth, alone among the planets of the Hutchinson and from the mind-wrenching growth with temperature is not negotiable; Solar System, had a carbon-based life and top-down view provided by NASA. chemistry,not biology,sets its constants. an industrial civilization. They would have Although welcomed by atmospheric At this stage, the Gaia theory was missing seen methane and oxygen coexisting in the scientists, Earth scientists were cautious. plausible control mechanisms. The first dis- upper atmosphere, and their chemists Biologists, especially Ford Doolittle and covered was a biological process that redressed would have known that these gases are Richard Dawkins, argued strongly that global the imbalance of the nutritious elements continually consumed and replaced. The self-regulation could never have evolved, as sulphur and iodine — these are abundant in odds of this happening by chance inorganic the organism was the unit of selection,not the the oceans, but deficient on the land surface.
    [Show full text]
  • Evidence That Eukaryotic Triosephosphate Isomerase Is of Alpha-Proteobacterial Origin
    Proc. Natl. Acad. Sci. USA Vol. 94, pp. 1270–1275, February 1997 Evolution Evidence that eukaryotic triosephosphate isomerase is of alpha-proteobacterial origin PATRICK J. KEELING* AND W. FORD DOOLITTLE Department of Biochemistry, Dalhousie University, Halifax, NS Canada, B3H 4H7 Communicated by Norman R. Pace, University of California, Berkeley, CA, December 10, 1996 (received for review July 8, 1996) ABSTRACT We have cloned and sequenced genes for nuclear genome. These genes most often resemble eubacterial triosephosphate isomerase (TPI) from the gamma-proteobac- homologues and are thought to have been transferred to the terium Francisella tularensis, the green non-sulfur bacterium nucleus from the symbiont genome, in most cases soon after Chloroflexus aurantiacus, and the alpha-proteobacterium Rhi- the endosymbiosis was established (11), although isolated zobium etli and used these in phylogenetic analysis with TPI instances of organelle to nucleus transfer occurring more sequences from other members of the Bacteria, Archaea, and recently in evolution can still be documented for both mito- Eukarya. These analyses show that eukaryotic TPI genes are chondria and plastids (12–15). most closely related to the homologue from the alpha- In nearly all widely accepted instances of such transfer, the proteobacterium and most distantly related to archaebacte- product of the transferred gene still functions in the organelle rial homologues. This relationship suggests that the TPI genes in which it originally resided. We are aware of only one clear present in modern eukaryotic genomes were derived from an case in which an organelle gene seems to have replaced a alpha-proteobacterial genome (possibly that of the protomi- nuclear homologue and assumed its cytosolic function.
    [Show full text]
  • The Epistemic Revolution Induced by Microbiome Studies: an Interdisciplinary View
    biology Review The Epistemic Revolution Induced by Microbiome Studies: An Interdisciplinary View Eric Bapteste 1,*, Philippe Gérard 2, Catherine Larose 3, Manuel Blouin 4 , Fabrice Not 5 , Liliane Campos 6 , Géraldine Aïdan 7, M. André Selosse 1,8 , M. Sarah Adénis 9, Frédéric Bouchard 10,Sébastien Dutreuil 11, Eduardo Corel 1, Chloé Vigliotti 12, Philippe Huneman 13, F. Joseph Lapointe 14 and Philippe Lopez 1 1 Institut de Systématique, Evolution, Biodiversité (ISYEB), Sorbonne Université, CNRS, Museum National d’Histoire Naturelle, EPHE, Université des Antilles, 75005 Paris, France; [email protected] (M.A.S.); [email protected] (E.C.); [email protected] (P.L.) 2 Micalis Institute, INRAE, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France; [email protected] 3 Environmental Microbial Genomics, Laboratoire Ampère, École Centrale de Lyon, CNRS, University of Lyon, 69134 Ecully, France; [email protected] 4 Département Agronomie Agroéquipements Elevage Environnement, UMR 1347 Agroécologie (INRA/AgroSup/Université de Bourgogne), 26 Bd Docteur Petitjean, BP 87999, CEDEX, 21079 Dijon, France; [email protected] 5 Sorbonne Université, CNRS, AD2M-UMR7144, Station Biologique de Roscoff, 29680 Roscoff, France; [email protected] 6 PRISMES—Langues, Textes, Arts et Cultures du Monde Anglophone—EA 4398, Université Sorbonne Nouvelle and Institut Universitaire de France, 75005 Paris, France; [email protected] 7 CERSA, UMR 7106 (CNRS—Université Paris II Panthéon-Assas), 10 rue Thénard, 75005 Paris, France; [email protected] 8 Citation: Bapteste, E.; Gérard, P.; Faculty of Biology, University of Gda´nsk,ul. Wita Stwosza 59, 80-308 Gda´nsk,Poland 9 PILI, 16 Avenue du Bas Meudon, 92130 Issy-les-Moulineaux, France; [email protected] Larose, C.; Blouin, M.; Not, F.; 10 Département de Philosophie, Université de Montréal, Montréal, QC H3C 3J7, Canada; Campos, L.; Aïdan, G.; Selosse, M.A.; [email protected] Adénis, M.S.; Bouchard, F.; et al.
    [Show full text]
  • Endosymbiosis and Its Implications for Evolutionary Theory
    Endosymbiosis and its implications for evolutionary theory Maureen A. O’Malley1 Department of Philosophy, University of Sydney, Sydney, NSW 2006, Australia Edited by W. Ford Doolittle, Dalhousie University, Halifax, NS, Canada, and approved March 24, 2015 (received for review December 21, 2014) Historically, conceptualizations of symbiosis and endosymbiosis and neo-Darwinian evolutionary theory form the contemporary have been pitted against Darwinian or neo-Darwinian evolutionary focus. Although her main arguments do not withstand much theory. In more recent times, Lynn Margulis has argued vigorously analysis, macroevolutionary considerations do seem to offer an along these lines. However, there are only shallow grounds for explanatory niche for endosymbiotic innovations. However, I will finding Darwinian concepts or population genetic theory incom- show that, when organelle-producing endosymbiotic relationships patible with endosymbiosis. But is population genetics suffi- are scrutinized further, the explanatory focus shifts to metabolism ciently explanatory of endosymbiosis and its role in evolution? and its evolutionary consequences. In the final part of the paper, I Population genetics “follows” genes, is replication-centric, and is will revisit the implications for evolutionary theory when addi- concerned with vertically consistent genetic lineages. It may also tional explanatory resources are gained for the modern synthesis have explanatory limitations with regard to macroevolution. Even from a metabolic interpretation of endosymbiosis. so, asking whether population genetics explains endosymbiosis may have the question the wrong way around. We should instead Historical Claims About Endosymbiosis be asking how explanatory of evolution endosymbiosis is, and ex- There is a long history of researchers who have theorized about actly which features of evolution it might be explaining.
    [Show full text]
  • Evidence That Eukaryotic Triosephosphate Isomerase Is of Alpha-Proteobacterial Origin
    Proc. Natl. Acad. Sci. USA Vol. 94, pp. 1270–1275, February 1997 Evolution Evidence that eukaryotic triosephosphate isomerase is of alpha-proteobacterial origin PATRICK J. KEELING* AND W. FORD DOOLITTLE Department of Biochemistry, Dalhousie University, Halifax, NS Canada, B3H 4H7 Communicated by Norman R. Pace, University of California, Berkeley, CA, December 10, 1996 (received for review July 8, 1996) ABSTRACT We have cloned and sequenced genes for nuclear genome. These genes most often resemble eubacterial triosephosphate isomerase (TPI) from the gamma-proteobac- homologues and are thought to have been transferred to the terium Francisella tularensis, the green non-sulfur bacterium nucleus from the symbiont genome, in most cases soon after Chloroflexus aurantiacus, and the alpha-proteobacterium Rhi- the endosymbiosis was established (11), although isolated zobium etli and used these in phylogenetic analysis with TPI instances of organelle to nucleus transfer occurring more sequences from other members of the Bacteria, Archaea, and recently in evolution can still be documented for both mito- Eukarya. These analyses show that eukaryotic TPI genes are chondria and plastids (12–15). most closely related to the homologue from the alpha- In nearly all widely accepted instances of such transfer, the proteobacterium and most distantly related to archaebacte- product of the transferred gene still functions in the organelle rial homologues. This relationship suggests that the TPI genes in which it originally resided. We are aware of only one clear present in modern eukaryotic genomes were derived from an case in which an organelle gene seems to have replaced a alpha-proteobacterial genome (possibly that of the protomi- nuclear homologue and assumed its cytosolic function.
    [Show full text]
  • Uprooting the Tree of Life W
    Uprooting the Tree of Life w. ford doolittle originally published in february 2000 C harles Darwin contended more than a century ago that all modern species diverged from a more limited set of ancestral groups, which themselves evolved from still fewer progenitors and so on back to the be- ginning of life. In principle, then, the relationships among all living and extinct organisms could be represented as a single genealogical tree. Most contemporary researchers agree. Many would even argue that the general features of this tree are already known, all the way down to the root—a solitary cell, termed life’s last universal common ancestor, that lived roughly 3.5 to 3.8 billion years ago. The consensus view did not come easily but has been widely accepted for more than a decade. Yet ill winds are blowing. To everyone’s surprise, discoveries made in the past few years have begun to cast serious doubt on some aspects of the tree, especially on the depiction of the relationships near the root. THE FIRST SKETCHES Scientists could not even begin to contemplate constructing a universal tree until about 35 years ago. From the time of Aristotle to the 1960s, re- searchers deduced the relatedness of organisms by comparing their anat- omy or physiology, or both. For complex organisms, they were frequently able to draw reasonable genealogical inferences in this way. Detailed analyses of innumerable traits suggested, for instance, that hominids shared a common ancestor with apes, that this common ancestor shared an earlier one with monkeys, and that that precursor shared an even ear- lier forebear with prosimians, and so forth.
    [Show full text]
  • W. Ford Doolittle: Evolutionary Provocations and a Pluralistic Vision
    W. Ford Doolittle: Evolutionary Provocations and a Pluralistic Vision This is the penultimate draft of a chapter to appear in Dreamers, Romantics and Visionaries in the Life Sciences, edited by Michael Dietrich and Oren Harman (forthcoming, University of Chicago Press). Please check first before citing or using this draft. Maureen A. O'Malley University of Bordeaux [email protected] Introduction Although many scientists see their work as distinct from academic endeavors that are not classified as natural science, others draw resources from more distant disciplines. Ford Doolittle has maintained throughout his career a deep interest in the humanities and arts, which might be explained to some extent by his father’s academic interests. His father was a professor of Art (painting) at the University of Illinois in Champaign-Urbana, the city in which Ford was born in 1942. As an undergraduate at Harvard, Doolittle was torn between science and literature. Science won, at least in part because his applications to literature programs were knocked back.1 When he was interviewed in 1970 for a position at Dalhousie University (Halifax, Nova Scotia, Canada), the Department Head asked him what he would do if he didn’t get the job. ‘Write science fiction’, said Doolittle, suggesting an alternative career that was not utterly unimaginable to people who knew him at the time.2 Non- counterfactually, Doolittle pursued part-time for several years a degree in Fine Arts at the Nova Scotia College of Art and Design (completed in 2012). Working in several media, his photography in particular has engaged with his scientific world-view and been exhibited in its own right.
    [Show full text]
  • Uprooting the Tree of Life Copyright 2000 Scientific American, Inc
    About 10 years ago scientists finally worked out Uprooting the basic outline of how the modern life-forms evolved. Now parts of their tidy Tree of Life scheme are unraveling by W.Ford Doolittle Instead of looking just at anatomy or physiology, they asked, why not base family trees on differences in the order of the building blocks in selected genes or proteins? harles Darwin contended more than a century Their approach, known as molecular phylogeny, is emi- ago that all modern species diverged from a nently logical. Individual genes, composed of unique se- more limited set of ancestral groups, which quences of nucleotides, typically serve as the blueprints for themselves evolved from still fewer progeni- making specific proteins, which consist of particular strings tors and so on back to the beginning of life. In of amino acids. All genes, however, mutate (change in se- C principle, then, the relationships among all liv- quence), sometimes altering the encoded protein. Genetic mu- ing and extinct organisms could be represented as a single ge- tations that have no effect on protein function or that im- nealogical tree. prove it will inevitably accumulate over time. Thus, as two Most contemporary researchers agree. Many would even species diverge from an ancestor, the sequences of the genes argue that the general features of this tree are already known, they share will also diverge. And as time passes, the genetic all the way down to the root—a solitary cell, termed life’s last divergence will increase. Investigators can therefore recon- universal common ancestor, that lived roughly 3.5 to 3.8 bil- lion years ago.
    [Show full text]
  • Simple and Complex Nuclear Loci Created by Newly Transferred Chloroplast DNA in Tobacco
    Simple and complex nuclear loci created by newly transferred chloroplast DNA in tobacco Chun Y. Huang*†, Michael A. Ayliffe‡, and Jeremy N. Timmis*§ *School of Molecular and Biomedical Science, University of Adelaide, Adelaide SA 5005, Australia; and ‡CSIRO Plant Industry, G.P.O. Box 1600, Canberra ACT 2601, Australia Edited by W. Ford Doolittle, Dalhousie University, Halifax, Canada, and approved May 21, 2004 (received for review February 6, 2004) Transfer of organelle DNA into the nuclear genome has been terium transformation (16–18). The involvement of this mech- significant in eukaryotic evolution, because it appears to be the anism also has been inferred in the nuclear integration of origin of many nuclear genes. Most studies on organelle DNA organelle DNA sequences (14), although the interpretation of transfer have been restricted to evolutionary events but experi- such analyses is complicated by the presence of many preexisting mental systems recently became available to monitor the process organelle sequences in the nucleus and potential postintegrative in real time. We designed an experimental screen to detect plastid rearrangement and sequence decay. With the advent of exper- DNA (ptDNA) transfers to the nucleus in whole plants grown under imental systems to detect de novo plastid DNA (ptDNA) transfer natural conditions. The resultant genotypes facilitated investiga- (19, 20), direct studies of the nuclear integration mechanisms are tion of the evolutionary mechanisms underlying ptDNA transfer possible for the first time. and nuclear integration. Here we report the characterization of We investigated plastid-to-nucleus DNA transfer in the prog- nuclear loci formed by integration of newly transferred ptDNA.
    [Show full text]