A spliceosomal intron of mitochondrial DNA origin

SummaryThe origin of spliceosomal introns is one of the most enduring mysteries in molecular biology. In nuclear genomes such as our own, the protein-coding regions of genes (exons) can be separated from one another by hundreds of thousands of base pairs (bp) of intronic (non-coding) DNA, and while they are often considered ‘junk’, introns are increasingly ascribed important regulatory functions [1]. Here we present evidence that an intron in a GTPase superfamily gene in the unicellular alga Bigelowiella natans is derived from — and was created by — the insertion of a fragment of mitochondrial DNA. Organelle-to-nucleus DNA transfer is an increasingly well-understood phenomenon, one that has the potential to greatly influence genome structure [2,3]. Our data suggest that such transfers could represent a hitherto underappreciated source of new spliceosomal introns

Lower algebraic K-theory of certain reflection groups

For a finite volume geodesic polyhedron P in hyperbolic 3-space, with the property that all interior angles between incident faces are integral submultiples of Pi, there is a naturally associated Coxeter group generated by reflections in the faces. Furthermore, this Coxeter group is a lattice inside the isometry group of hyperbolic 3-space, with fundamental domain the original polyhedron P. In this paper, we provide a procedure for computing the lower algebraic K-theory of the integral group ring of such Coxeter lattices in terms of the geometry of the polyhedron P. As an ingredient in the computation, we explicitly calculate some of the lower K-groups of the dihedral groups and the product of dihedral groups with the cyclic group of order two.Comment: 35 pages, 2 figure

Total hemispherical emittance measured at high temperatures by the calorimetric method

A calorimetric vacuum emissometer (CVE) capable of measuring total hemispherical emittance of surfaces at elevated temperatures was designed, built, and tested. Several materials with a wide range of emittances were measured in the CVE between 773 to 923 K. These results were compared to values calculated from spectral emittance curves measured in a room temperature Hohlraum reflectometer and in an open-air elevated temperature emissometer. The results differed by as much as 0.2 for some materials but were in closer agreement for the more highly-emitting, diffuse-reflecting samples. The differences were attributed to temperature, atmospheric, and directional effects, and errors in the Hohlraum and emissometer measurements (plus or minus 5 percent). The probable error of the CVE measurements was typically less than 1 percent

Algal genomes reveal evolutionary mosaicism and the fate of nucleomorphs

Cryptophyte and chlorarachniophyte algae are transitional forms in the widespread secondary endosymbiotic acquisition of photosynthesis by engulfment of eukaryotic algae. Unlike most secondary plastid-bearing algae, miniaturized versions of the endosymbiont nuclei (nucleomorphs) persist in cryptophytes and chlorarachniophytes. To determine why, and to address other fundamental questions about eukaryote–eukaryote endosymbiosis, we sequenced the nuclear genomes of the cryptophyte Guillardia theta and the chlorarachniophyte Bigelowiella natans. Both genomes have \u3e21,000 protein genes and are intron rich, and B. natans exhibits unprecedented alternative splicing for a single-celled organism. Phylogenomic analyses and subcellular targeting predictions reveal extensive genetic and biochemical mosaicism, with both host- and endosymbiont-derived genes servicing the mitochondrion, the host cell cytosol, the plastid and the remnant endosymbiont cytosol of both algae. Mitochondrion-to-nucleus gene transfer still occurs in both organisms but plastid-to-nucleus and nucleomorph-to-nucleus transfers do not, which explains why a small residue of essential genes remains locked in each nucleomorph

Low Earth orbital atomic oxygen environmental simulation facility for space materials evaluation

Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administrations's (NASA) Lewis Research Center provides accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analyses show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (approximately 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4 x 10 exp 6 atoms/((sq. cm)*s), thus providing a highly accelerated testing capability

The effects of ethanol intoxication on phobic anxiety

Behavioral conceptions of alcohol abuse often include the hypothesis that drinking behavior is a negatively reinforced operant, with ethanol intoxication viewed as alleviating aversive environmental and internal states. This hypothesis has not been confirmed or refuted by previous studies which employed mild stressors and limited assessment methodology. In the present experiment, 22 patients with severe phobias approached their phobic animal under two consecutive conditions--first while sober and second after drinking either a placebo or an intoxicating dose of ethanol. The severe anxiety induced was assessed behaviorally, physiologically and by the patient's self-report of fear. The intoxicated patients did not experience decreased anxiety, tachycardia or avoidance, compared to the placebo group. These results have clinical implications and suggest the need to reconsider tension-reduction theories of alcohol abuse.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25019/1/0000446.pd

The repeated pretest-posttest single-subject experiment: A new design for empirical clinical practice

The logic of a new design for empirical clinical practice, the repeated pretest-posttest experiment, is described. This design is readily applicable by individual practitioners in the human services, possesses high internal validity, and presents minimal intrusiveness into the delivery of service. A single-case study is used to illustrate the application of the repeated pretest-posttest experiment in clinical research.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25047/1/0000475.pd

Arc-textured metal surfaces for high thermal emittance space radiators

Carbon arc electrical discharges struck across the surfaces of metals such as Nb-1 percent Zr, alter the morphology to produce a high thermal emittance surface. Metal from the surface and carbon from the arc electrode vaporize during arcing, and then condense on the metal surface to produce a microscopically rough surface having a high thermal emittance. Quantitative spectral reflectance measurements from 0.33 to 15 microns were made on metal surfaces which were carbon arc treated in an inert gas environment. The resulting spectral reflectance data were then used to calculate thermal emittance as a function of temperature for various methods of arc treatment. The results of arc treatment on various metals are presented for both ac and dc arcs. Surface characterization data, including thermal emittance as a function of temperature, scanning electron microscopy, and atomic oxygen durability, are also presented. The ac arc texturing was found to increase the thermal emittance at 800 K from 0.05 to 0.70

Complete Sequence and Analysis of the Mitochondrial Genome of Hemiselmis andersenii CCMP644 (Cryptophyceae)

<p>Abstract</p> <p>Background</p> <p>Cryptophytes are an enigmatic group of unicellular eukaryotes with plastids derived by secondary (i.e., eukaryote-eukaryote) endosymbiosis. Cryptophytes are unusual in that they possess four genomes–a host cell-derived nuclear and mitochondrial genome and an endosymbiont-derived plastid and 'nucleomorph' genome. The evolutionary origins of the host and endosymbiont components of cryptophyte algae are at present poorly understood. Thus far, a single complete mitochondrial genome sequence has been determined for the cryptophyte <it>Rhodomonas salina</it>. Here, the second complete mitochondrial genome of the cryptophyte alga <it>Hemiselmis andersenii </it>CCMP644 is presented.</p> <p>Results</p> <p>The <it>H. andersenii </it>mtDNA is 60,553 bp in size and encodes 30 structural RNAs and 36 protein-coding genes, all located on the same strand. A prominent feature of the genome is the presence of a ~20 Kbp long intergenic region comprised of numerous tandem and dispersed repeat units of between 22–336 bp. Adjacent to these repeats are 27 copies of palindromic sequences predicted to form stable DNA stem-loop structures. One such stem-loop is located near a GC-rich and GC-poor region and may have a regulatory function in replication or transcription. The <it>H. andersenii </it>mtDNA shares a number of features in common with the genome of the cryptophyte <it>Rhodomonas salina</it>, including general architecture, gene content, and the presence of a large repeat region. However, the <it>H. andersenii </it>mtDNA is devoid of inverted repeats and introns, which are present in <it>R. salina</it>. Comparative analyses of the suite of tRNAs encoded in the two genomes reveal that the <it>H. andersenii </it>mtDNA has lost or converted its original <it>trnK(uuu) </it>gene and possesses a <it>trnS</it>-derived '<it>trnK(uuu)</it>', which appears unable to produce a functional tRNA. Mitochondrial protein coding gene phylogenies strongly support a variety of previously established eukaryotic groups, but fail to resolve the relationships among higher-order eukaryotic lineages.</p> <p>Conclusion</p> <p>Comparison of the <it>H. andersenii </it>and <it>R. salina </it>mitochondrial genomes reveals a number of cryptophyte-specific genomic features, most notably the presence of a large repeat-rich intergenic region. However, unlike <it>R. salina</it>, the <it>H. andersenii </it>mtDNA does not possess introns and lacks a Lys-tRNA, which is presumably imported from the cytosol.</p