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At least 199 records · Page 11Linked to original sources
PubMed1981

Presence of intranuclear micro cables in a primitive dinoflagellate protist: morphological description and discussion of their possible evolutionary significance.

An intranuclear "cable" system has been demonstrated in the nucleus of the so-called primitive dinoflagellate Prorocentrum micans E. by means of a new cryofixation technique. Numerous cables are situated between the chromosomes. They are composed of several helically twisted filaments of 50-60 A diameter. The diameter of the cables varies from 200 A. In most dinoflagellates the microtubular spindle is permanently extranuclear, whereas this filament system is always located in the nucleus and is permanently surrounded by the nuclear envelope. The possible function of these cables is discussed. In evolutionary terms, such a complex fibrillar system must be taken into account as much as the microtubular system, particularly in these cells which are still considered as lower eukaryotes, although the special position of the dinoflagellates becomes more and more separate.

Animals↗
PubMed1981

The enigmatic protist Nephromyces.

This paper review current knowledge concerning the identity of Nephromyces, a collection of fungus-like cells found in the renal sac of all molgulid tunicates thus far examined. The following has been demonstrated: (1) The cells called Nephromyces do exist, and are not produced by their tunicate hosts, but are something foreign to these animals. (2) Many forms of "Nephromyces" cells are present simultaneously in the renal sac of adults of each molgulid species. Despite their extraordinarily eclectic appearance, all these cells are part of the same life cycle. (3) Initial ultrastructural data indicate that Nephromyces is a eukaryote. They also suggest that, despite the speculations of early authors, Nephromyces may not be a Chytridiomycete.

Fungi↗
PubMed1988

Assessment of phylogenetic relationships among ciliated protists using partial ribosomal RNA sequences derived from reverse transcripts.

Partial sequences were derived for the 16S-like ribosomal RNA of Halteria grandinella, Glaucoma chattoni, Colpidium campylum, Opisthonecta henneguyi and Colpoda inflata. Using isolated bulk nucleic acid preparations, partial rRNA sequences were determined using a series of oligonucleotide primers complementary to conserved sequence elements of the molecule and a dideoxynucleotide sequencing reaction using reverse transcriptase. Sequences were aligned and an evolutionary tree was generated by a distance-matrix method, comparing these partial sequences to the complete sequences of species of Tetrahymena, Paramecium, Euplotes, Oxytricha and Stylonychia. Halteria shows greater similarity to the stichotrichs Oxytricha and Stylonychia than to the hypotrich Euplotes, while these four genera share the same branch. Glaucoma and Colpidium appear closely related to Tetrahymena, with all three being more closely related to Opisthonecta than to Paramecium. Colpoda diverges near the base of the branch shared by Paramecium and the four oligohymenophorean genera. These results are discussed with reference to published revisions of the systematics of the phylum Ciliophora.

Animals↗
PubMed1986

Length variation in eukaryotic rRNAs: small subunit rRNAs from the protists Acanthamoeba castellanii and Euglena gracilis.

We have sequenced the region of the Acanthamoeba castellanii ribosomal RNA transcription unit which encodes the mature small subunit ribosomal RNA (SSU rRNA). It, like the SSU rRNA coding regions of Euglena gracilis and kinetoplastids, is approx. 30% larger than those reported from other eukaryotes. The extra nucleotides are present in highly variable regions of the rRNA genes. Direct sequence analysis of the corresponding variable regions in the rRNA of A. castellanii and E. gracilis demonstrates that the extra nucleotides are present in the mature rRNA; no post-transcriptional modification of the rRNAs occurs to reduce them to a size more typical of eukaryotes. The extra elements present in the rRNAs of these two organisms are not homologous; they have independent evolutionary origins.

Amoeba↗
PubMed1991

Sequence and organization of 5S RNA genes from the eukaryotic protist Acanthamoeba castellanii.

A 5S RNA genomic clone has been isolated from Acanthamoeba castellanii and the sequence of the coding region plus flanking DNA was determined. This clone encodes an RNA whose sequence matches that of 5S RNA from this organism. There is sequence similarity in the 5'-flanking region to other eukaryotic 5S RNA genes which require or are greatly affected by upstream regions for transcriptional activity. The immediate 3'-flanking region has a termination sequence similar to that found in all genes that are transcribed by RNA polymerase III. The 5S RNA genes of A. castellanii are dispersed, which is highly unusual, since the majority of eukaryotic organisms contain 5S genes clustered in tandem repeats. There may be up to 480 genes encoding 5S RNA in each A. castellanii cell.

Acanthamoeba↗
PubMed2005

Acute toxicity of heavy metals towards freshwater ciliated protists.

The acute toxicity of five heavy metals to four species of freshwater ciliates (Colpidium colpoda, Dexiotricha granulosa, Euplotes aediculatus, and Halteria grandinella) was examined in laboratory tests. After exposing the ciliates to soluble compound of cadmium, copper, chromium, lead, and nickel at several selected concentrations, the mortality rate was registered and the LC50 values (with 95% confidence intervals) were calculated. Large differences appeared in sensitivities of the four species to the metals. H. grandinella showed the highest sensitivity for cadmium (0.07 mg l(-1), LC50) and lead (0.12 mg l(-1), LC50), whilst E. aediculatus showed the highest sensitivity for nickel (0.03 mg l(-1), LC50). The comparison with data obtained with other species indicate that Halteria grandinella and Euplotes aediculatus are excellent and convenient bioindicator for evaluating the toxicity of waters and wastewaters polluted by heavy metals. The short time (24 h) and simplicity of the test procedure enable this test to be used in laboratory studies.

Animals↗
PubMed2004

Chromatin from two classes of platyhelminthes display both protist H1 and higher eukaryote core histones.

Histones from the parasitic platyhelminthes, Echinococcus granulosus and Fasciola hepatica, were systematically characterized. Core histones H2A, H2B, H3 and H4, which were identified on the basis of amino acid sequencing and mass spectrometry data, showed conserved electrophoretic patterns. Histones H1, identified on the basis of physicochemical properties, amino acid composition and amino acid sequencing, showed divergence, both in their number and electrophoretic mobilities, between the two species and among other organisms. According to these data, core histones but not H1 histones, would be stabilized during evolution at the level of platyhelminthes.

Amino Acid Sequence↗
PubMed2004

Two novel asparaginyl endopeptidase-like cysteine proteinases from the protist Trichomonas vaginalis: their evolutionary relationship within the clan CD cysteine proteinases.

Cysteine proteinases (CPs) are important virulence factors of the protozoan parasite Trichomonas vaginalis. A total of six genes coding for cathepsin L-like CPs belonging to clan CA have been identified in T. vaginalis. At least 23 distinct spots with proteolytic activity have been detected by two-dimensional (2-D) substrate gel electrophoresis from in vitro grown parasites; however, only few of them have been characterized. In this work, we detected six spots with proteolytic activity and molecular weights between 25 and 35 kDa. The six proteinases correspond to two distinct CP families: the papain-like family, represented by four spots with pIs between 4.5 and 5.5; and the legumain-like family represented by two spots with pI 6.3 and 6.5. Next, we obtained two cDNAs encoding for legumain-like CPs from T. vaginalis, which were named Tvlegu-1 and Tvlegu-2. The size of these cDNA clones were 1225 and 1364 bp, which encoded for 388 and 415 amino acids, respectively. Their putative translation products have molecular masses of 42.8 and 47.2 kDa, corresponding to inactive legumain-like CP precursors. The two sequences share approximately 40% identity at the amino acid level. These protein products can be classified within a branch of the legumain-like family in clan CD cysteine proteinases due to their sensitivity to specific proteinases inhibitors, their DNA sequences, and phylogenetic reconstruction. However, they do not correspond either to the typical asparaginyl endopeptidase or the glycosylphosphatidylinositol (GPI): protein transamidase subfamilies. These results suggest that the TVLEGU-1 and TVLEGU-2 peptidases are likely to be part of a new subfamily within the legumain-like family of clan CD cysteine proteinases. Furthermore, they could be one of the missing links between prokaryotic and eukaryotic CPs in clan CD enzymes.

Amino Acid Sequence↗
PubMed2005

Identification, structure, and phylogenetic relationships of a mitogen-activated protein kinase homologue from the parasitic protist Entamoeba histolytica.

A gene encoding mitogen-activated protein kinase (MAPK) from the human enteric parasite, Entamoeba histolytica has been identified. Sequence analyses of the polymerase chain reaction (PCR) and reverse transcription PCR (RT-PCR) products reveal that the EhMAPK gene is intronless and encodes a protein of 352 amino acids. EhMAPK shows significant homology with other MAPKs and contains the 11 subdomains including the invariant residues characteristic of serine/threonine protein kinases. The MAPK signature residues and motifs are also present in EhMAPK. The atomic model of EhMAPK built with rat ERK2 as template exhibits the conservation of all major secondary structural features. However, a deletion in close proximity to the dual phosphorylation/activation site is of particular interest as it may have functional implications. Phylogenetic analysis indicates that EhMAPK is tightly clustered with Giardia intestinalis ERK2 and Dictyostelium discoideum ERK2. Detailed sequence analysis and phylogenetic study aided us to postulate that EhMAPK belongs to the extracellular signal-regulated kinase (ERK) family. Although EhMAPK bears good homology and phylogenetic closeness with human ERK8 and rat ERK7, sequence analysis indicates that they may be functionally different. The significant differences such as the deletions in the vicinity of the phosphorylation lip, variations in the P+1 specificity pocket, presence of additional acidic amino acids in the common docking domain provide a ground for postulations that activators and substrates for EhMAPK may be to some extent divergent from that of the ERKs of the mammalian host. Although functional characterization of EhMAPK remains to be done, this is the first study of any member of the MAPK signaling system in this organism.

Amino Acid Sequence↗
PubMed2001

Microsporidia: emerging pathogenic protists.

Microsporidia are eukaryotic spore forming obligate intracellular protozoan parasites first recognized over 100 years ago. These organisms infect all of the major animal groups and are now recognized as opportunistic pathogens of humans. Microsporidian spores are common in the environment and microsporidia pathogenic to humans have been found in water supplies. The genera Nosema, Vittaforma, Brachiola, Pleistophora, Encephalitozoon, Enterocytozoon, Septata (reclassified to Encephalitozoon) and Trachipleistophora have been found in human infections. These organisms have the smallest known eukaryotic genomes. Microsporidian ribosomal RNA sequences have proven useful as diagnostic tools as well as for phylogenetic analysis. Recent phylogenetic analysis suggests that Microsporidia are related to the fungi. These organisms are defined by the presence of a unique invasion organelle consisting of a single polar tube that coils around the interior of the spore. All microsporidia exhibit the same response to stimuli, that is, the polar tube discharges from the anterior pole of the spore in an explosive reaction. If the polar tube is discharged next to a cell, it can pierce the cell and transfer its sporoplasm into the cell. A technique was developed for the purification of polar tube proteins (PTPs) using differential extraction followed by reverse phase HPLC. This method was used to purify the PTPs from Glugea americanus, Encephalitozoon cuniculi, Enc. hellem and Enc. intestinalis. These PTPs demonstrate conserved characteristics such as solubility, hydrophobicity, mass, proline content and immunologic epitopes. The major PTP gene from Enc. cuniculi and Enc. hellem has been cloned and expressed in vitro. The gene sequences support the importance of ER and in the formation of the polar tube as suggested by morphologic studies. Analysis of the cloned proteins also indicates that secondary structural characteristics are conserved. These characteristics are probably important in the function of this protein during the eversion/assembly of the polar tube and in providing elasticity and resiliency for sporoplasm passage.

Amino Acid Sequence↗
PubMed2001

Transport of aspartic acid, arginine, and tyrosine by the opportunistic protist Pneumocystis carinii.

In order to improve culture media and to discover potential drug targets, uptake of an acidic, a basic, and an aromatic amino acid were investigated. Current culture systems, axenic or co-cultivation with mammalian cells, do not provide either the quantity or quality of cells needed for biochemical studies of this organism. Insight into nutrient acquisition can be expected to lead to improved culture media and improved culture growth. Aspartic acid uptake was directly related to substrate concentration, Q(10) was 1.10 at pH 7.4. Hence the organism acquired this acidic amino acid by simple diffusion. Uptake of the basic amino acid arginine and the aromatic amino acid tyrosine exhibited saturation kinetics consistent with carrier-mediated mechanisms. Kinetic parameters indicated two carriers (K(m)=22.8+/-2.5 microM and K(m)=3.6+/-0.3 mM) for arginine and a single carrier for tyrosine (K(m)=284+/-23 microM). The effects of other L-amino acids showed that the tyrosine carrier was distinct from the arginine carriers. Tyrosine and arginine transport were independent of sodium and potassium ions, and did not appear to require energy from ATP or a proton motive force. Thus facilitated diffusion was identified as the mechanism of uptake. After 30 min of incubation, these amino acids were incorporated into total lipids and the sedimentable material following lipid extraction; more than 90% was in the cellular soluble fraction.

Arginine↗
PubMed2005

Mitochondrion-derived organelles in protists and fungi.

The mitochondrion is generally considered to be a defining feature of eukaryotic cells, yet most anaerobic eukaryotes lack this organelle. Many of these were previously thought to derive from eukaryotes that diverged prior to acquisition of the organelle through endosymbiosis. It is now known that all extant eukaryotes are descended from an ancestor that had a mitochondrion and that in anaerobic eukaryotes the organelle has been modified into either hydrogenosomes, which continue to generate energy for the host cell, or mitosomes, which do not. These organelles have each arisen independently several times. Recent evidence suggests a shared derived characteristic that may be responsible for the retention of the organelles in the absence of the better-known mitochondrial functions--iron-sulfur cluster assembly. This review explores the events leading to this new understanding of mitochondrion-derived organelles in amitochondriate eukaryotes, the current state of our knowledge, and future areas for investigation.

Animals↗