1,720,966 research outputs found
Protein transport into the nucleus: characterization of nuclear localization signals in the protozoan ciliate Euplotes
No full textEvidence 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
Protein transport into the nucleus: characterization of nuclear localization signals in the protozoan ciliate Euplotes
No full textIn E. raikovi, a nuclear protein kinase, designated Er-MAPK1, appears to be phosphorylated in association with the mechanism of signal transduction which promotes cell proliferation through autocrine interactions between cell type-specific signaling protein pheromones and their membrane receptors. This kinase shows significant structural matching to mammalian kinases that are localized in the nucleus of specialized cell types, such as the "Male germ cell-Associated Kinases" and the "Intestinal Cell Kinases". Two Arg/Lys-rich motifs were identified in the Er-MAPK1 C-terminal domain as putative “nuclear localization signals” and their effective function in directing this protein into the nucleus was studied by expressing GFP-tagged protein constructs in mammalian fibroblasts. The results obtained provide evidence that distant related organisms such as ciliates and mammals use the same molecular language for the nuclear translocation and localization of proteins, suggesting that this language arose early in the evolution of the eukaryotic cell
Evolution of the intracellular transport mechanisms in eukaryotes: ciliates and mammals use the same translocation and nuclear localization signals
Full text linkIn the ciliate E. raikovi, self/non-self recognition phenomena are controlled by cell type-specific, water-borne signal proteins (pheromones) by their binding to target cell-surface receptors. The downstream signal transduction pathway activated by the pheromone-receptor interactions of self type (that promote the vegetative, mitogenic cell growth) involves the phosphorylation of a nuclear protein kinase, designated Er-MAPK1, which is structurally similar to the "intestinal-cell kinase" and "male germ cell-associated kinase" described in mammals. To identify the sequence segments responsible for Er-MAPK1 nuclear localization, mouse fibroblasts were transfected with plasmids containing the reporter gene for the "Green-Fluorescent Protein" (GFP) associated to different fragments of the Er-MAPK1 coding sequence. By expressing GFP-tagged protein constructs in mammalian cells, in the C-terminal domain of Er-MAPK1 it was effectively possible to identify an Arg/Lys-rich motif that is required for the nuclear entry of GFP-fused constructs. These results provide evidence that distant related organisms such as ciliates and mammals use the same molecular language for the nuclear translocation and localization of proteins, thus suggesting that this language arose early in the evolution of the eukaryotic cell
Characterization and Expression of the Gene Encoding En-MAPK1, an Intestinal Cell Kinase (ICK)-like Kinase Activated by the Autocrine Pheromone-Signaling Loop in the Polar Ciliate, Euplotes nobilii
Full text linkIn the protozoan ciliate Euplotes, a transduction pathway resulting in a
mitogenic cell growth response is activated by autocrine receptor binding of cell
type-specific, water-borne signaling protein pheromones. In Euplotes raikovi, a marine
species of temperate waters, this transduction pathway was previously shown to involve
the phosphorylation of a nuclear protein kinase structurally similar to the intestinal-cell and
male germ cell-associated kinases described in mammals. In E. nobilii, which is
phylogenetically closely related to E. raikovi but inhabits Antarctic and Arctic waters, we
have now characterized a gene encoding a structurally homologous kinase. The expression
of this gene requires +1 translational frameshifting and a process of intron splicing for the
production of the active protein, designated En-MAPK1, which contains amino acid
substitutions of potential significance for cold-adaptation
Mutual benefits from the symbiotic coexistence between bipolar Euplotes cells and Parafrancisella bacteria
No full textCiliates are common carriers of cytoplasmic bacteria, however little is known about the molecular basis of the symbiotic relationships with their host. Working on interbreeding bipolar (Arctic and Antarctic) populations of the ciliate Euplotes nobilii, members of these populations were found to stably host Parafrancisella γ-proteobacteria. These bacteria (originally isolated from an Antarctic population of another Euplotes species, E. petzi) are phylogenetically related to pathogenic Francisella species which are well known for their capacity to colonize eukaryotic cells, causing animal diseases known as francisellosis. The finding that Parafrancisella/Euplotes associations are common in polar marine environments suggested that both microbial partners benefit from their stable partnership. To inquire into mutual advantages, we carried out a genomic analysis of E. nobilii and its Parafrancisella symbionts. In the E. nobilii genome, no gene was detected encoding methionine sulfoxide reductase of type A (MsrA), an enzyme which is essential to face damages from oxidative stress imposed by the high (saturated) oxygen concentrations of the polar sea waters. At the same time, the Parafrancisella genome revealed genes encoding MsrA sequences endowed with a N-terminal signal peptide for the secretion into the host’s cytoplasm, and the effectiveness of this secretion was further supported by the identification of a complete gene set coding for the so-called ‘Type VI Secretion System’ that many Gram-negative bacteria use to transfer their proteins into target cells. On the other side, in the Parafrancisella genome no gene encoding enzymes involved in the biosynthetic pathways of cysteine, lysine, methionine, and threonine was detected, implying that Parafrancisella cells rely on their E. nobilii host to obtain these four essential amino acids
The Sub-Chromosomic Macronuclear Pheromone Genes of the Ciliate Euplotes raikovi: Comparative Structural Analysis and Insights into the Mechanism of Expression
No full textIn Euplotes raikovi, we have determined the full-length sequences of a family of macronuclear genes that are the transcriptionally active versions of codominant alleles inherited at the mating-type (mat) locus of the micronuclear genome, and encode cell type-distinctive signaling pheromones. These genes include a 225-231-bp coding region flanked by a conserved 544-bp 5'-leader region and a more variable 3'-trailer region. Two transcription initiation start sites and two polyadenylation sites associated with nonconventional signals cooperate with a splicing phenomenon of a 326-bp intron residing in the 5'-leader region in the generation of multiple transcripts from the same gene. In two of them, the synthesis of functional products depends on the reassignment to a sense codon, or readthrough of a strictly conserved leaky UAG stop codon. That this reassignment may take place is suggested by the position this codon occupies in the transcripts, close to the transcript extremity and far from the poly(A) tail. In such a case, one product is a 69-amino acid protein in search of function and the second product is a 126-amino acid protein that represents a membrane-bound pheromone isoform candidate to function as a cell type-specific binding site (receptor) of the soluble pheromones
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
- …
