1,720,958 research outputs found
Trasferimento genico orizzontale da batteri a nuclei eucariotici: un esempio nel ciliato Euplotes.
No full textLa trasmissione di geni tra organismi filogeneticamente distanti è ormai considerato un fenomeno, noto come “horizontal, or lateral gene transfer”, tra i più rilevanti nell’indirizzare l’evoluzione biologica. Sembrano esservi coinvolti tutti gli organismi, più diffusamente quelli che vivono in endosimbiosi. Ad essere trasmessi sono sia geni codificanti proteine responsabili della duplicazione genica, sia geni codificanti enzimi citoplasmatici implicati nel metabolismo cellulare. Uno di questa seconda categoria di geni è stato identificato, e denominato msrAB, nel genoma macronucleare
(sinteticamente attivo) di Euplotes raikovi, in relazione a uno studio strutturale e funzionale del complesso genico che presiede la sintesi di enzimi riparatori delle reazioni ossidative cui vanno incontro le macromolecole biologiche in seguito a danni metabolici e invecchiamento cellulare.
msrAB è uno dei vari geni che E. raikovi utilizza per sintetizzare le due forme, A e B, di metioninasolfossido reduttasi (Msr) deputate a ridurre i residui di metionina ossidati di una proteina di nuovo a residui non ossidati. A sostegno della sua origine proteobatterica sta il fatto che la sequenza aminoacidica MsrA che esso codifica ha un’identità dell’85% con la sequenza di MsrA di Sinorhizobium meliloti. L’integrazione strutturale e funzionale di msrAB nel genoma macronucleare di E. raikovi è invece dimostrata dal fatto che le estremità telomeriche di questo gene presentano la ripetizione dell’eptanucleotide C4A4 distintiva di tutti i mini-cromosomi (“gene-sized molecules”) che compongono il genoma macronucleare di Euplotes
Evidence for methionine-sulfoxide-reductase gene transfer from Alphaproteobacteria to the transcriptionally active (macro)nucleus of the ciliate, Euplotes raikovi.
Full text linkBackground: Deleterious phenomena of protein oxidation affect every aerobic organism and methionine residues are their elective targets. The reduction of methionine sulfoxides back to methionines is catalyzed by
methionine-sulfoxide reductases (Msrs), enzymes which are particularly active in microorganisms because of their
unique nature of individual cells directly exposed to environmental oxidation.
Results: From the transcriptionally active somatic genome of a common free-living marine protist ciliate, Euplotes raikovi, we cloned multiple gene isoforms encoding Msr of type A (MsrA) committed to repair methionine-S-sulfoxides. One of these isoforms, in addition to including a MsrA-specific nucleotide sequence, included also a sequence specific for a Msr of type B (MsrB) committed to repair methionine-R-sulfoxides. Analyzed for its structural relationships with MsrA and MsrB coding sequences of other organisms, the coding region of this gene
(named msrAB) showed much more significant relationships with Msr gene coding sequences of Rhodobacterales and
Rhizobiales (Alphaproteobacteria), than of other eukaryotic organisms.
Conclusions: Based on the fact that the msrAB gene is delimited by Euplotes-specific regulatory 5′ and 3′ regions and telomeric C4A4/G4T4 repeats, it was concluded that E. raikovi inherited the coding region of this gene through a phenomenon of horizontal gene transfer from species of Alphaproteobacteria with which it coexists in nature and on
which it likely feeds
Polar and non-polar species of the protozoan ciliate Euplotes behave differently in response to environmental oxidative stress
Full text linkPolar coastal seawaters are saturated by high oxygen concentrations, which impose very effective adaptive strategies to strive against a continuous environmental oxidative stress. We studied these strategies in Euplotes nobilii (Ciliophora: Spirotrichea), a ciliate species dwelling in Antarctic and Arctic coastal seawaters, in comparison with Euplotes raikovi, a sister species living in temperate seawaters. Cell samples of the two species were exposed to hydrogen peroxide (H2O2)-induced oxidative stress and analyzed for their survival rates and levels of expression of the genes encoding the enzyme methionine-sulfoxide reductase (Msr) A, which restores oxidized methionines (in their S form) of damaged proteins to the status of functional methionines. While 6 h of exposure to a 750-μM concentration of H2O2 did not affect E. nobilii viability, these conditions were lethal to E. raikovi. In correlation with this inter-specific difference in the cell survival to oxidative stress, the MsrA-coding genes of the two species showed different mechanisms of expression: constitutive in E. nobilii, elicited by induction in E. raikovi
The water-borne protein signals (pheromones) of the Antarctic ciliated protozoan, Euplotes nobilii: structure of the gene coding for the En-6 pheromone
No full textThe marine Antarctic ciliate, Euplotes nobilii, secretes a family of water-borne signal proteins, denoted as pheromones, that control the cell vegetative proliferation and mating. Based on the knowledge of the amino acid sequences of a set of these pheromones isolated from the culture supernatant of wild-type strains, we designed probes to identify their encoding genes represented by linear sub-chromosomic (gene-sized) DNA molecules in the somatic nucleus (macronucleus) of the cell. The full-length gene of the pheromone En-6 was determined and found to contain an open reading frame specific for the synthesis of the En-6 cytoplasmic precursor (pre-pro-En-6), that requires two proteolytic cleavages to remove the signal-peptide (pre) and the pro segment before secretion of the mature protein. In contrast to from the sequence variability that distinguishes the secreted pheromones, the pre and pro sequences appear to be tightly conserved and useful to construct probes to clone every other E. nobilii pheromone gene. Potential intron sequences in the coding region of the En-6 gene imply the synthesis of more En-6 isoforms
Caratterizzazione dei geni dei feromoni di Euplotes nobilii, un ciliato antartico.
No full textAnalogamente ad alcune altre specie di Euplotes, E. nobilii (originariamente raccolto dalle acque marine costiere antartiche e, più recentemente, anche artiche da F. Dini e coll.) è in grado di secernere nell’ambiente proteine-segnale (denominate feromoni) deputate a regolare sia la riproduzione cellulare (moltiplicazione mitotica), sia il processo sessuale della coniugazione, mediante interazioni di tipo autocrino e paracrino con specifici recettori di membrana. Dopo aver purificato quattro diversi feromoni di E. nobilii ed averne determinato la struttura anche a livello tridimensionale (Pedrini et al., 2007, J. Mol. Biol., 372: 277-286), ci siamo interessati alla caratterizzazione dei rispettivi geni codificanti, previa identificazione mediante tecniche di amplificazione genica. Questi geni si compongono di circa 1000 nucleotidi e le loro regioni regolative in 5’ e 3’ sono sostanzialmente equivalenti. Analogamente ai geni dei feromoni di E. raikovi e E. octocarinatus, anch’essi sintetizzano i feromoni sotto forma di precursori citoplasmatici, in cui si riconoscono tre regioni funzionalmente distinte: un “peptide segnale” di 19 amino acidi, una regione “pro” di 12, e una regione corrispondente alla proteina “matura” di 52-63. Per la secrezione del feromone (proteina matura) sono quindi richiesti due tagli proteolitici, il primo relativo alla rimozione co-traduzionale del peptide segnale, e il secondo relativo alla rimozione post-traduzionale del segmento “pro”. Mentre le regioni della proteina matura presentano variazioni strutturali significative, le strutture del peptide segnale e della regione “pro” sono strettamente conservate
Invecchiamento cellulare e riparazione del danno ossidativo nel ciliato Euplotes raikovi: caratterizzazione dei geni specifici per le metionina-solfossido redattasi
No full textCiliated protozoa represent excellent material to explore the biology of ageing and rejuvenation, since they are both “complex” organisms and “simple” cells directly exposed at the environment and natural selection. Using Euplotes raikovi (a protistan whose life cycle is well characterized), I investigated the molecular resources that enable cells to repair oxidative damage of their vital macromolecules. A complex of six distinct genes that encode two forms, A and B, of methionine sulphoxide redutase (Msr, the enzyme that reduces a residue of methionine sulphoxide to methionine) was identified. The complete structure of two of these genes (designated Er-msrB and Er-msrA/B) was determined including both coding and non-coding regions; the structural analysis of the other four genes (Er-msrA1, Er-msrA2-A, Er-msrA2-B, e Er-msrA2-C) was incomplete. Er-MsrB2 (specified by one of the two open reading frames of the Er-msrA/B gene), Er-MsrB1, and Er-MsrA1 are closely related to Msr’s of other protozoa. In contrast, Er-msrA3 (specified by the second open reading frame of the Er-msrA/B gene) and Er-MsrA2 are phylogenetically related to Msr’s of prokaryotic origin. A further divergence between the Er-msr genes was detected at the functional level. Transcription of the Er-msrB gene is apparently not induced by oxidative stress, whereas transcription of the genes encoding the Msr A forms is specifically enhanced in cells subjected to oxidative stres
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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