Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PARAMECIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1978

Ultrastructure of the proximal region of somatic cilia in Paramecium tetraurelia.

The morphology of the transition zone between the terminal plate of the basal body and the 9 + 2 region of the somatic (non-oral) cilium has been examined in Paramecium tetraurelia. Freeze-fracture and thin-section techniques disclosed both membrane specializations and various internal structural linkages. Freeze-fracture material revealed sets of particles interrupting the unit membrane. The more distal of these form plaquelike arrays while the proximal set of particles forms the ciliary "necklace." The plaque regions correspond to anionic sites on the outer membrane surface as revealed by binding of polycationic ferritin. Both the plaque particles and the necklace particles appear to be in contact with outer doublet microtubules via a complex of connecting structures. In the interior of the transition zone an axosomal plate supports an axosome surrounded by a ring of lightly packed material. Only one of the two central tubules of the axoneme reaches and penetrates the axosome. Below the axosomal plate four rings, each approx. 20 nm wide, connect adjacent outer doublets. An intermediate plate lies proximal to these rings, and a terminal plate marks the proximal boundary of this zone. Nine transitional fibers extend from the region of the terminal plate to the plasmalemma. The observations described above have been used to construct a three-dimensional model of the transition region of "wild-type" Paramecium somatic cilia. It is anticipated that this model will be useful in future studies concerning possible function of transition-zone specializations, since Paramecium may be examined in both normal and reversed ciliary beating modes, and since mutants incapable of reverse beating are available.

Animals↗
PubMed1979

Sodium uptake and membrane excitation in Paramecium.

Although the phenotypes of many membrane-excitation mutants of Paramecium are best expressed in Na+-containing solutions, little is known about the role of Na+ in membrane excitation in Paramecium. By measuring 22Na fluxes, we have shown that: (a) The total cellular Na+ content is equivalent to a cytoplasmic concentration of 3--4 mM, if the Na+ concentration is uniform throughout the cell. (b) The kinetics of Na+ uptake can be divided into a saturable Na+ uptake with an apparent Km = 0.15 mM and a nonsaturable Na+ uptake seen at higher Na+ concentrations up to 20 mM. (c) The rate of Na+ uptake in high Na+ solutions is correlated with the duration of backward swimming and membrane excitation in wild type Paramecium and the mutants fast-2 and paranoiac. (d) Na+ uptake is inhibited at 4 degrees C. From these results, we postulate that Na+ uptake is faster when the membrane is depolarized than when it is at the resting potential level.

Animals↗
PubMed1983

Intra- and interspecific complementation of membrane-inexcitable mutants of Paramecium.

Membrane excitation was the basis for backward swimming of Paramecium facing stimulus. According to standard genetic tests, inexcitable mutants fell into three complementation groups for both Paramecium tetraurelia (pwA, pwB, and pwC) and Paramecium caudatum (cnrA, cnrB, and cnrC). Cytoplasm from a wild type transferred to a mutant through microinjection restored the excitability. Transfusions between genetically defined complementation groups of the same species effected curing, whereas transfusions between different mutants (alleles) of the same group or between sister cells of the same mutant clone did not. Cytoplasmic transfers of all combinations among the six groups of mutants of the two species showed that any cytoplasm, except those from the same group, was able to cure. Since the pawns and the caudatum nonreversals complement one another through transfusion, they appeared to belong to six different complementation groups. The extent of curing, the amount of transfer needed to cure, and the time course of curing were characteristic of the group that received the transfusion. Variations in these parameters further suggested that the six groups represented six different genes. Because the donor cytoplasms from either species were equally effective quantitatively in curing a given mutant, the curing factors were not species specific. These factors are discussed.

Animals↗
PubMed1967

Binding of Ca ions by Paramecium caudatum.

Binding of (45)Ca by live Paramecium caudatum was determined under various external ionic conditions. It was found that calcium uptake was separable into at least two components, a rapid and a slow one. The rapid component was influenced by the presence of certain other ions in a manner which agrees with the law of mass action. It appears that an ion exchange system may be involved in a binding equilibrium established between Paramecium, Ca(++), and certain other ions. K(+), Rb(+), and Ba(++) in the equilibrium medium are among those ions which inhibit calcium uptake. It is proposed that liberation of Ca(++) from binding sites on Paramecium by an exchange reaction with competing ions is the first step in the mechanism of ciliary reversal in the response to external application of these ions.

Animals↗
PubMed1998

Homology-dependent gene silencing in Paramecium.

Microinjection at high copy number of plasmids containing only the coding region of a gene into the Paramecium somatic macronucleus led to a marked reduction in the expression of the corresponding endogenous gene(s). The silencing effect, which is stably maintained throughout vegetative growth, has been observed for all Paramecium genes examined so far: a single-copy gene (ND7), as well as members of multigene families (centrin genes and trichocyst matrix protein genes) in which all closely related paralogous genes appeared to be affected. This phenomenon may be related to posttranscriptional gene silencing in transgenic plants and quelling in Neurospora and allows the efficient creation of specific mutant phenotypes thus providing a potentially powerful tool to study gene function in Paramecium. For the two multigene families that encode proteins that coassemble to build up complex subcellular structures the analysis presented herein provides the first experimental evidence that the members of these gene families are not functionally redundant.

Animals↗
PubMed1998

Tubulin polyglycylation: differential posttranslational modification of dynamic cytoplasmic and stable axonemal microtubules in paramecium.

Polyglycylation, a posttranslational modification of tubulin, was discovered in the highly stable axonemal microtubules of Paramecium cilia where it involves the lateral linkage of up to 34 glycine units per tubulin subunit. The observation of this type of posttranslational modification mainly in axonemes raises the question as to its relationship with axonemal organization and with microtubule stability. This led us to investigate the glycylation status of cytoplasmic microtubules that correspond to the dynamic microtubules in Paramecium. Two anti-glycylated tubulin monoclonal antibodies (mAbs), TAP 952 and AXO 49, are shown here to exhibit different affinities toward mono- and polyglycylated synthetic tubulin peptides. Using immunoblotting and mass spectrometry, we show that cytoplasmic tubulin is glycylated. In contrast to the highly glycylated axonemal tubulin, which is recognized by the two mAbs, cytoplasmic tubulin reacts exclusively with TAP 952, and the alpha- and beta- tubulin subunits are modified by only 1-5 and 2-9 glycine units, respectively. Our analyses suggest that most of the cytoplasmic tubulin contains side chain lengths of 1 or 2 glycine units distributed on several glycylation sites. The subcellular partition of distinct polyglycylated tubulin isoforms between cytoplasmic and axonemal compartments implies the existence of regulatory mechanisms for glycylation. By following axonemal tubulin immunoreactivity with anti-glycylated tubulin mAbs upon incubation with a Paramecium cellular extract, the presence of a deglycylation enzyme is revealed in the cytoplasm of this organism. These observations establish that polyglycylation is reversible and indicate that, in vivo, an equilibrium between glycylating and deglycylating enzymes might be responsible for the length of the oligoglycine side chains of tubulin.

Amino Acid Sequence↗
PubMed1998

A mutation in Paramecium tetraurelia reveals functional and structural features of developmentally excised DNA elements.

The excision of internal eliminated sequences (IESs) from the germline micronuclear DNA occurs during the differentiation of a new macronuclear genome in ciliated protozoa. In Paramecium, IESs are generally short (28-882 bp), AT rich DNA elements that show few conserved sequence features with the exception of an inverted-terminal-repeat consensus sequence that has similarity to the ends of mariner/Tcl transposons (KLOBUTCHER and HERRICK 1995). We have isolated and analyzed a mutant cell line that cannot excise a 370-bp IESs (IES2591) from the coding region of the 51A variable surface protein gene. A single micronuclear C to T transition within the consensus sequence prevents excision. The inability to excise IES259 I has revealed a 28-bp IES inside the larger IES, suggesting that reiterative integration of these elements can occur. Together, the consensus sequence mutation and the evidence for reiterative integration support the theory that Paramecium IESs evolved from transposable elements. Unlike a previously studied Paramecium IES, the presence of this IES in the macronucleus does not completely inhibit excision of its Mild-type micronuclear copy through multiple sexual generations.

Animals↗
PubMed1983

Isolation and translation of mRNA coding for the variant surface antigens of Paramecium.

In the poly(A)+RNA isolated from the ciliate Paramecium primaurelia is found a discrete and abundant mRNA species of high molecular weight (corresponding to about 9,000 nucleotides). This mRNA species has size and abundance characteristics that identify it tentatively as the message coding for the variant cell-surface antigens. After microinjection of the high molecular weight mRNA into amphibian oocytes, polypeptides are synthesized that are immunoprecipitated specifically with antibodies directed against the homologous Paramecium antigen. On collecting the culture medium of oocytes microinjected with Paramecium mRNA, newly-synthesized complete antigen molecules (Mr approximately 300,000) can be recovered by immunoprecipitation.

Animals↗
PubMed1990

Nucleotide sequence of the mitochondrial genome of Paramecium.

The nucleotide sequence for 40,469 bp of the linear Paramecium aurelia mitochondrial (mt) genome is presented with the locations of the known genes, presumed ORFs, and their transcripts. Many of the genes commonly encoded in mt DNA of other organisms have been identified in the Paramecium mt genome but several unusual genes have been found. Ribosomal protein genes rps14, rps12, and rpl2 are clustered in a region that also contains two other genes usually found in chloroplasts, but rpl14 is over 16 kbp away. The ATP synthase gene, atp9, is encoded in this mt genome, but the atp6, atp8, and COIII genes have not been identified. All of the identified genes are transcribed. Many mono- and poly- cistronic transcripts have been detected which cover most of the genome, including large regions where genes have yet to be identified. Based on sequence comparisons with known tRNAs, only those for phe, trp, and tyr are encoded in Paramecium mt DNA.

Animals↗
PubMed1992

A repetitive DNA sequence in Paramecium macronuclei is related to the beta subunit of G proteins.

A repeated DNA sequence has been identified in the macronucleus of several Paramecium species. In P.tetraurelia the repeat was identified in the subtelomeric region of four randomly selected telomere clones, as well as downstream of the A type variable surface protein gene. The complete sequence of the A gene linked repeat consists of 15 tandem repeats of exactly 126 nucleotides that contain an open reading frame with significant similarity to the beta subunits of trimeric G proteins. The most striking consensus feature is the amino acid sequence DX omega WD where X is any amino acid and omega is I, L, or V spaced at precise 42 amino acids intervals. This sequence and spacing are found in G-protein beta subunits and other members of this protein motif family. Analysis of the five cloned telomeric restriction fragments showed the repeats can be found in either orientation with respect to the telomere. Poly(A) RNA transcripts containing this sequence have been identified in Paramecium tetraurelia. The conserved presence of this sequence in several species of Paramecium suggests an important physiological function, and the study of this repeat may reveal information about the evolution of this common protein motif.

Amino Acid Sequence↗
PubMed1992

Purification, characterization and structure of protein phosphatase 1 from the cilia of Paramecium tetraurelia.

A type 1 serine/threonine protein phosphatase (PP1) which is mostly localized in the excitable ciliary membranes from the protozoan Paramecium, was purified to homogeneity. Approximately 4 micrograms enzyme of 37 kDa was isolated from 100 l axenic culture. The enzymic properties were characterized using phosphorylase a from rabbit skeletal muscle as a substrate and several known effectors of mammalian PP1. The protozoan PP1 was enzymically indistinguishable from its mammalian congener. The amino acid sequence of the Paramecium PP1 was deduced from its cDNA. The full-length clone was obtained in several steps starting with a pair of degenerate primers made according to the two most conserved peptides of rabbit PP1 and PP2A. The gene encodes a protein of 36,392 Da. The identity of the cloned gene and the isolated ciliary PP1 was unequivocally established by microsequencing of four tryptic and cyanogen-bromide peptides which were generated from the purified protein. Paramecium PP1 shows 75% amino-acid-sequence identity with rabbit PP1 alpha. Areas of major differences are the C-termini and N-termini and a sequence between residues 219-242.

Amino Acid Sequence↗
PubMed1994

New non-lethal calmodulin mutations in Paramecium. A structural and functional bipartition hypothesis.

The mechanisms by which calmodulin coordinates its numerous molecular targets in living cells remain largely unknown. To further understand how this pivotal Ca(2+)-binding protein functions in vivo, we isolated and studied nine new Paramecium behavioral mutants defective in calmodulin. Nucleotide sequences of mutant calmodulin genes indicated single amino-acid substitutions in mutants cam4(E104K), cam5-1 (D95G), cam6 (A102V), cam7 (H135R), cam14-1 (G59S) and cam15 (D50G). In addition, we encountered a second occurrence of three identified substitutions; they are cam1-2 (S101F), cam5-2 (D95G) and cam14-2 (G59S). Most of these mutational changes occurred in sites that have been highly conserved throughout evolution. Furthermore, most of these changes were not among the amino acids known to interact with the basic amphiphilic peptides of calmodulin targets. Consistent with our previous finding [Kink, J. A., Maley, M. E., Preston R. R., Ling, K.-Y., Wallen-Friedman, M. A., Saimi, Y. & Kung, C. (1990) Cell 62, 165-174], mutants that under-reacted to certain stimuli (allele number above 10) had substitutions in the N-terminal lobe of calmodulin, and those that over-reacted (below 10) had substitutions in the C-terminal lobe. No mutations were found in the central helix that connects the lobes. Thus, through undirected in vivo mutation analyses of Paramecium, we discovered that each of the two lobes of calmodulin has a distinct role in regulating the function of a specific ion channel and eventually the behavior of Paramecium. We, therefore, propose a hypothesis of functional bipartition of calmodulin that reflects its structural bipartition.

Alleles↗
PubMedDate not supplied

Analysis of Paramecium macronuclear DNA using pulsed field gel electrophoresis.

We have analyzed the macronuclear DNA of Paramecium tetraurelia using orthogonal-field-alternation gel electrophoresis. The mean size of the linear macronuclear DNA molecules is approximately 450 kb. Less than 6% of the macronuclear DNA is larger than 800 kb. Using pulse times of 20, 40, 60 and 90 s we show that the macronuclear fragment containing the A type variable surface antigen gene migrates reproducibly as a 320-kb linear DNA. Over the same pulse times we describe the unusual migration of the ribosomal RNA gene (rDNA) of P. tetraurelia. At pulse times of 20 and 40 s the rDNA migrates at limit mobility (300 and 500 kb, respectively) whereas with 60- and 90-s pulse times, 2 components of rDNA are observed; 1 fraction independent of pulse time migrating at limit mobility, and a 2nd component migrating between 100-kb and 400-kb linear markers. Based upon previous electron micrographic studies of Paramecium rDNA as well as data presented here we conclude that the majority of Paramecium rDNA molecules are a circular DNA form.

Animals↗
PubMedDate not supplied

Effect of SERCA pump inhibitors on chemoresponses in Paramecium.

Inhibitors of SERCA (sarcoplasmic/endoplasmic reticulum Ca(2+)-dependent ATPase) calcium pumps were used to investigate the involvement of internal Ca2+ stores in the GTP response in Paramecium. External application of these inhibitors was found to dramatically alter the typical behavioral and electrophysiological responses of Paramecium to extracellular chemical stimulation. In particular, 2,5-di-tert-butylhydroquinone (BHQ) strongly inhibited the backward swimming response of paramecia to externally applied GTP, though it did not inhibit the associated whirling response. BHQ also prolonged the normally brief electro-physiological response of these cells to GTP. BHQ completely blocked the behavioral and electrophysiological responses of Paramecium to extracellular Ba2+, but had no measurable effect on the behavioral or electrophysiological responses of these cells to another depolarizing stimulus, elevated external K+ concentration. These results suggest the involvement of nonciliary Ca2+ ions in the GTP and Ba2+ responses.

Animals↗
PubMedDate not supplied

A novel member of the cyclin-dependent kinase family in Paramecium tetraurelia.

Passage through the cell cycle in eukaryotes requires the successive activation of different cyclin-dependent protein kinases. Here, we describe the identification and characterization of a novel class of cyclin-dependent protein kinase, termed Cdk2, in the ciliate Paramecium tetraurelia. It is 301 amino acids long, 7 amino acids shorter than Cdk1, the CDK that is associated with macronuclear DNA synthesis. All the catalytic domains typical of protein kinases can be located within the sequence and putative regulatory phosphorylation sites equivalent to Thr14, Tyr15, and Thr161 in human CDK1 are also conserved. The 'PSTAIRE' region characteristic of most CDKs is perfectly conserved. Cdk2 shares only 48% homology to Cdk1 at the amino acid level, suggesting that the evolutionary separation of Cdk1 and Cdk2 is ancient, and implying that they have different roles in cell cycle regulation. Like Cdk1, Cdk2 does not bind to yeast p13suc1, even though it has better conservation of p13suc1 binding sites than Cdk1 does. The Cdk2 protein level is relatively constant throughout the vegetative cell cycle. Cdk2 exhibits kinase activity towards bovine histone H1 in vitro with the maximal level late in the cell cycle, suggesting it may be involved in the regulation of cytokinesis. Our results further support the view that an analogue of the cyclin-dependent kinase cell cycle regulatory system like that of yeast and higher eukaryotic cells operates in Paramecium and that a family of cyclin-dependent kinases may control different aspects of the Paramecium cell cycle.

Amino Acid Sequence↗
PubMedDate not supplied

Fine oral filaments in Paramecium: a biochemical and immunological analysis.

In Paramecium, several kinds of the oral networks of fine filaments are defined at the ultrastructural level. Using the sodium chloride-treated oral apparatus of Paramecium as an antigen to produce monoclonal antibodies, we have begun to identify the proteins constituting these networks. Immunoblotting showed that all positive antibodies were directed against three bands (70-, 75-and 83-kD), which corresponded to quantitatively minor components of the antigen; there was no antibody specific for the quantitatively major components (58- and 62-kD). Immunolocalization with four of these antibodies directed against one or several of these three bands showed that these proteins are components of the fine filaments supporting the oral area; a decoration of the basal bodies and the outer lattice was also observed on the cortex. Immunofluorescence on interphase cells suggested that the three proteins colocalized on the left side of the oral apparatus, whereas only the 70-kD band was detected on the right side. During division, the antigens of the antibodies were detected at different stages after oral basal body assembly. The antibodies cross-reacted with the tetrins, which are oral filament-forming proteins in Tetrahymena, demonstrating that tetrin-related proteins are quantitatively minor components of the oral and the somatic cytoskeleton of Paramecium.

Animals↗
PubMedDate not supplied

Electrokaryotypes of macronuclei of several Paramecium species.

A comparative study of macronuclear DNA molecules from the following Paramecium species: the P. aurelia complex, P. caudatum, P. bursaria, P. putrinum and P. multimicronucleatum was performed using pulsed-field gel electrophoresis. The electrophoretic pattern was constant and unique for each species, and is referred to herein as its electrokaryotype. Large differences were observed between Paramecium species according to the range and major size of macronuclear DNA fragments, while different strains of the same species, even belonging to different syngens, were characterized by the same electrokaryotype. In this respect sibling species from the P. aurelia complex are as similar as syngens in other Paramecium species, but are unlike conventional species. The principles and value of electrokaryotype analysis for application to ciliates are discussed.

Animals↗
PubMedDate not supplied

G-protein modulators alter the swimming behavior and calcium influx of Paramecium tetraurelia.

To assess the potential role of G-proteins in chemokinesis, Paramecium tetraurelia was pre-incubated with the G-protein modulator pertussis toxin. Pertussis toxin pretreatment significantly reduced Paramecium chemoattraction to sodium acetate and ammonium chloride in T-maze behavioral assays and depressed the frequency of avoidance reactions, indicating that heterotrimeric G-proteins may be involved with the motility response. To determine whether G-proteins exert their effect via the ciliary voltage-sensitive calcium channel, we examined responses of P. tetraurelia to the potent voltage-sensitive calcium channel agonist, deltamethrin. Pertussis toxin preincubation significantly reduced the toxic effects of deltamethrin exposure as determined by survival under depolarizing conditions and reduced the duration of backward swimming episodes in behavioral bioassays. Furthermore, non-hydrolyzable analogs of guanine nucleotides altered deltamethrin-stimulated calcium influx via calcium channels in isolated ciliary vesicles. Heterotrimeric G-protein subunits were subsequently detected in ciliary vesicles of P. tetraurelia by antibodies produced against Galpha and Gbeta subunits, and by 32P-ADP-ribosylation, indicating that proteins of the appropriate molecular weight are the target of pertussis toxin in these vesicles. These findings provide additional evidence that heterotrimeric G-proteins are associated with ciliary vesicles and that they play a role in the modulation of swimming behavior and the toxic action of deltamethrin in Paramecium.

Animals↗