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PubMed1994

Hairpin and dimer structures of linear plasmid-like DNAs in mitochondria of Paramecium caudatum.

The molecular structure of plasmid-like DNAs (designated type-II) which were isolated from mitochondria in the ciliated protozoan Paramecium caudatum was characterized. These type-II DNAs are always detected as a set of four kinds with sizes of 8.2, 4.1, 2.8 and 1.4 kb. The DNAs of 8.2 and 2.8 kb exist as dimers consisting of 4.1- and 1.4-kb monomer molecules, respectively. Electron microscopic observations indicated configurations of a hairpin structure that had a protruding end of single-stranded DNA in one terminus and a loop in the other terminus. The monomers stick together with base-pairing in opposite directions at the protruding end to form the dimers, suggesting the presence of inverted repeats. These unusual dimers may have a role in replication of the DNAs in which the monomers can serve as a primer for each other.

Animals↗
PubMed1987

Structure and sequence of the H surface protein gene of Paramecium and comparison with related genes.

The serotype H immobilization antigen (H i-ag) gene of Paramecium tetraurelia was isolated from a genomic library by screening with the H i-ag transcript. The gene is 7.5 kb long and contains no introns. Similar to other i-ag genes, it does not undergo rearrangement or duplication upon expression. In contrast, only the H i-ag gene appears to be non-adjacent to a telomere. Sequence comparisons between the H, A, and C i-ag genes of stock 51 and the G i-ag gene of stock 156 identify conserved upstream sites and extensive homology in the 3' non-coding region. Several of these sites may be involved in regulating the expression of the i-ags. Segments of amino acid homology among these genes are also predicted by the DNA sequences.

Amino Acid Sequence↗
PubMed1981

Macronuclear chromatin organization in Paramecium primaurelia.

Chromatin organization and transcriptional activity in the macronucleus of the ciliate Paramecium primaurelia have been studied by electron microscopic examination of spread chromatin preparations. Under spreading conditions which inhibit the activity of endogenous nucleases and proteases, various morphologically distinct types of chromatin are seen: (1) Largely condensed chromatin in the form of 30-40 nm supranucleosomal globules which aggregate to form knobbly 40-60 nm fibres and unravel into 12 nm nucleosomal filaments; (2) In rapidly growing cells, extended chromatin arranged groups of 4-8 adjacent nucleofilaments, each bearing numerous and very densely packed lateral fibrils. These fibrils are 20 nm thick, have a smooth outline and extend to lengths of up to 3 micron. Such transcripts are grouped in units along the chromatin axis and are apparently organized in register in adjacent filaments; (3) In starved cells, extended nucleofilaments bearing only occasional RNP fibrils. These various morphological characteristics are discussed in terms of macronuclear transcriptional activity and the polyploid nature of macronuclei.

Animals↗
PubMed1976

Gene controlled selection of mitochondria in Paramecium.

The slow growing mutant cl1 of Paramecium, previously described (Sainsard, Claisse and Balmefrezol, 1974) differs from wild-type by a single recessive nuclear mutation and by a particular mitonchondrial phenotype (Mcl) that gene cl1 distinguishes from the wild-type mitochondrial phenotype (M+). A further analysis of these nucleo-mitochondrial interactions was carried out by confronting the genes cl1 and cl)+ with mixed populations of M+ and Mcl mitochondria obtained after cytoplasmic exchange at conjugation. The following results were obtained: 1. M+ and Mcl mitochondria introduced respectively into mutant and wild-type cells do not multiply easily; 2. when a mixed population (M+ + Mcl) is established, both mitochondrial types are maintained during the growth of the F1 heterozygous cl1/cl1+ clones; 3. when the nuclear segregation occurs in F2, the formation of homozygotes cl1/cl1 or cl1+/cl1+ is soon followed by the segregation of the two mitochondrial types, Mcl or M+, reconstituting the two parental nucleo-mitochondrial associations.

Crosses, Genetic↗
PubMed1978

Selection and characterization of nuclear mutations affecting mitochondria in Paramecium.

A screening method, based upon resistance to a tetrazolium salt (TTC), is described which permitted the isolation in Paramecium of 28 mutants resistant to TTC. These mutants displayed various defects in mitochondrial functions (cytochromic content cyanide insensitive respiration). Some mutations seemed to affect directly the respiration chain while others seemed to cause indirect modifications, possibly altering mitochondrial protein synthesis. Genetic analysis of four mutants showed in all that the resistance to TTC was of nuclear origin.

Animals↗
PubMed1980

Anatomy of mitochondrial DNA from Paramecium aurelia.

The linear genome of mitochondrial DNA from four species of Paramecium aurelia was investigated with respect to restriction endonuclease fragments, location and number of ribosomal RNA genes, and interspecies EcoRI and HindIII fragment homologies. One copy of each of the rRNA genes was found in all four species and the 14s and 20s rRNA genes were separated by at least 3,000 bp. R-Loop analysis of the 20s rRNA gene did not reveal the presence of an intervening sequence. Interspecies homology studies showed species 1, 5, and 7 to have a high degree of homology but species 4 was less than 50% homologous to species 1 mt DNA. For all four species, rRNA genes showed good homology indicating that these DNA sequences are highly conserved, even between species having many non-homologous regions. A major region of DNA which displayed little homology between species 1 and 4 was that fragment containing sequences essential for initiation of DNA replication.

Animals↗
PubMed1993

Ca2+ transport and chemoreception in Paramecium.

Intracellular Ca2+ levels in Paramecium must be tightly controlled, yet little is understood about the mechanisms of control. We describe here indirect evidence that a phosphoenzyme intermediate is the calmodulin-regulated plasma membrane Ca2+ pump and that a Ca(2+)-ATPase activity in pellicles (the complex of cell body surface membranes) is the enzyme correlate of the plasma membrane pump protein. A change in Ca2+ pump activity has been implicated in the chemoresponse of paramecia to some attractant stimuli. Indirect support for this is demonstrated using mutants with different modifications of calmodulin to correlate defects in chemoresponse with altered Ca2+ homeostasis and pump activity.

Animals↗
PubMed1978

Species identification in protozoa: glucosephosphate isomerase variation in the Paramecium aurelia group.

Results are presented for intra- and interspecies variation in electrophoretic mobility of the enzyme glucosephosphate isomerase in the Paramecium aurelia species complex. Three new observations have been made: (1) the hitherto indistinguishable species 1 and 5 can be distinguished on the basis of GPI electrophoretic mobility, (2) the degree of intraspecies variation is much higher for GPI than for the previously studied mitochondrial dehydrogenases and esterases, and (3) several of the enzymatic variants observed in one species are apparently indistinguishable from some found in other species. The intraspecies variants found have been shown to be allelic, and, on the basis of the enzyme patterns of the heterozygotes, it is proposed that GPI is a dimeric enzyme determined by two loci. In view of the use of enzyme variation as a means of species identification in protozoa, these results suggest that the use of such methods can lead to underestimating the number of species and possibly to misclassification. The implications of these findings together with the results obtained with Tetrahymena are discussed.

Animals↗
PubMed1980

Genetic control of lactate dehydrogenase isozymes in Paramecium caudatum.

The LDH isozymes were surveyed in bacterized cultures of syngens 1, 3, 12, and 13 of Paramecium caudatum by polyacrylamide gel electrophoresis. All the examined stocks of different syngens except one stock in syngen 3 had a single common LDH isozyme, and intra- and intersyngenic variation was not observed except for the one stock in syngen 3. Breeding data using the exceptional stock indicated that the LDH isozymes of P. caudatum are controlled by two codominant alleles at a single locus whose products aggregate randomly, forming a dimer.

Alleles↗
PubMed1983

Enhanced membrane fluorescence of CDC-labelled paramecium subsequent to removal of surface components.

Cytofluorimetric analysis of cycloheptaamylose-dansyl chloride (CDC) labelled Paramecium indicates that after mild trypsin removal of surface components the localization of CDC on the outer surface of living cells was not modified by the treatment. After such treatment the intensity of fluorescence emission was found about 3-fold higher in treated single cell than in the untreated one. These findings indicate that CDC labelling can be used to follow alteration occurred on the membrane of the living cell prior to labelling.

Animals↗
PubMed1975

X-ray microanalysis of calcium binding sites in Paramecium with special reference to exocytosis.

In Paramecium cells Ca++-stimulated triggering of the exocytosis of secretory vesicles ("trichocysts") was achieved by ionophores X-537 A or A 23187. Under triggering conditions electron dense deposits were present in some "resting" trichocysts and regularly in discharging trichocysts; upon subsequent fixation deposits occurred on the trichocyst membrane (on the inner side or within the membrane) and on the "inner lamellar sheath" from where deposits seemed to "radiate" into the secretory materials. Similar results were obtained with glutardialdehyde fixation alone which also triggers exocytosis but only at low concentrations. Element analysis by energy dispersive x-ray microanalysis ascertained the presence of Ca and P in deposits occurring in trichocysts. Those "resting" trichocysts which were devoid of deposits did not contain Ca or P enriched. Hence, an abrupt Ca++-influx into individual trichocysts just before exocytosis seems to be involved in the triggering mechanism, possible in combination with the sudden activation of an ATPase system localized at those sites of the trichocysts which primarily contain the deposits. When paramecia were treated only with Ca++ and then fixed with OsO4 plus oxalate or merely with glutardialdehyde, electron scattering deposits were formed also on the inner side of the cell membrane and within the ciliary shaft (but rarely in trichocysts). Deposits obtained on cilia (including "ciliary granule plaques") also contained Ca, P and S. Cells contain osmiophilic "calcium-storing vacuoles" which were selectively rich in Ca and S but devoid of P.

Animals↗
PubMed1988

L-glutamate-induced membrane hyperpolarization and behavioural responses in Paramecium tetraurelia.

Paramecium tetraurelia is attracted to L-glutamic acid concentrations of 10(-9) M to 10(-4) M in a behavioural assay. Electrophysiological studies show that P. tetaurelia responds to L-glutamate application with hyperpolarization. This response is transient, even in the continued presence of the stimulus. The concentration dependence of the membrane potential response is similar to that of the behavioural responses, although the threshold concentration of L-glutamate required for hyperpolarization is three orders of magnitude lower than for attraction. The membrane potential response to L-glutamate persists following artificial deciliation of P. tetraurelia. While application of L-glutamate to P. tetraurelia invariably elicits a hyperpolarization, withdrawal of the stimulus frequently results in a second transient membrane response, in the form of either a hyperpolarization or a depolarization. It is suggested that these 'off-responses' may have a significant role in maintaining a behavioural response to L-glutamate.

Animals↗
PubMed1987

Chemoreception in Paramecium tetraurelia: acetate and folate-induced membrane hyperpolarization.

Acetic and folic acids hyperpolarize the membrane potential of Paramecium tetraurelia in a concentration-dependent manner. The membrane responses are accompanied by small changes in cell resistance, and are significantly reduced by increasing extracellular cation concentrations, suggesting that the attractants bring about the membrane potential change by increasing cell permeability to cations. The inability to show a reversal potential for the hyperpolarization to attractants suggests that the effects of cations on the response are non-specific, however. The possible roles of Ca++, K+, and Na+ in the attractant-induced responses were further investigated by applying acetate and folate to cells with genetic defects in specific ion conductances, by collapsing the driving forces for these ions, and by testing the effects of ion channel blockers on the responses. These studies suggest that the membrane responses to attractants are not due to the direct effects of increased or decreased membrane permeability to cations. Attempts to block the acetate and folate-induced hyperpolarization by collapsing surface potential or using a mutant with reduced surface charge were inconclusive, as were studies on the possible role of attractant transport in the membrane responses. We hypothesize that the membrane hyperpolarization may be due to either the indirect effects of increased calcium permeability, to extrusion of calcium through activation of a calcium pump, or to a proton efflux.

Acetates↗
PubMed1979

The effect of temperature on copper tolerance of Paramecium.

The copper tolerance of paramecium tetraurelia decreases with increased temperatures over the range of 12 C to 34 C. The relationship is linear and the correlation = - 0.98. The regression equation has an intercept of 16 micro M Cu++ at O C, and tolerance is reduced by 0.33 micro M for each degree increase in temperature.

Animals↗
PubMed1990

Evidence for two K+ currents activated upon hyperpolarization of Paramecium tetraurelia.

Hyperpolarization of voltage-clamped Paramecium tetraurelia in K+ solutions elicits a complex of Ca2+ and K+ currents. The tail current that accompanies a return to holding potential (-40 mV) contains two K+ components. The tail current elicited by a step to -110 mV of greater than or equal to 50-msec duration contains fast-decaying (tau approximately 3.5 msec) and slow-decaying (tau approximately 20 msec) components. The reversal potential of both components shifts by 55-57 mV/10-fold change in external [K+], suggesting that they represent pure K+ currents. The dependence of the relative amplitudes of the two tail currents on duration of hyperpolarization suggests that the slow K+ current activates slowly and is sustained, whereas the fast current activates rapidly during hyperpolarization and then rapidly inactivates. Iontophoretic injection of a Ca2+ chelator, EGTA, specifically reduces slow tail-current amplitude without affecting the fast tail component. Both K+ currents are inhibited by extracellular TEA+ in a concentration-dependent, noncooperative manner, whereas the fast K+ current alone is inhibited by 0.7 mM quinidine.

Animals↗
PubMed1990

Interactions between mutants with defects in two Ca2(+)-dependent K+ currents of Paramecium tetraurelia.

Paramecium tetraurelia possesses two Ca2(+)-dependent K+ currents, activated upon depolarization IK(Ca,d), or upon hyperpolarization IK(Ca,h). The two currents are mediated by pharmacologically distinct ion channel populations. Three mutations of P. tetraurelia affect these currents. Pantophobiac A mutations (pntA) cause calmodulin sequence defects, resulting in the loss of both Ca2(+)-dependent K+ currents. A second mutation, TEA-insensitive A (teaA), greatly enhances IK(Ca,d) but has no affect on IK(Ca,h). A third mutation, restless (rst), also increases IK(Ca,d) slightly, but its principle effect is in causing an early activation of IK(Ca,h). Interactions between the products of these three genes were investigated by constructing three double mutants. Both teaA and rst restore IK(Ca,d) and IK(Ca,h) in pantophobiac A1, but the phenotypes of teaA and rst are not corrected by a second mutation. These observations may indicate a role for the gene products of teaA and rst in regulating the activity of IK(Ca,d) and IK(Ca,h), respectively.

Animals↗
PubMed1976

Mutants with reduced Ca activation in Paramecium aurelia.

Two heat-sensitive "pawn" mutants of Paramecium aurelia are capable of avoiding reactions when grown at 23 degrees C but not at 35 degrees C. Electrophysiological analyses show that Ca activation is reduces in the mutants even when they are grown at 23 degrees C. The maximal rate of rise and the peak of the evoked action potential (Ca-spike) in the mutants are smaller than those of wild type in a K-solution. After suppression of K conductance by either TEA+ or Ba++, the action potentials of the mutants peak at the same level as that of wild type. However, the maximal rate of rise of the mutants remains only about half that of wild type. Thus, the mutations affect Ca activation but not K activation. Incubation at a high temperature (35 degrees C) further reduces Ca activation to almost zero in the mutants but has little or no effect on wild type. This almost complete loss of Ca activation explains the lack of avoiding reactions when the mutants are grown at high temperatures. A double mutant containing two heat-sensitive mutations shows extremely reduced Ca activation even when grown at 23 degrees C.

Action Potentials↗
PubMed1987

A calcium-dependent potassium current is increased by a single-gene mutation in Paramecium.

The membrane currents of wild type Paramecium tetraurelia and the behavioral mutant teaA were analyzed under voltage clamp. The teaA mutant was shown to have a greatly increased outward current which was blocked completely by the combined use of internally delivered Cs+ and external TEA+. This, along with previous work (Satow, Y., Kung, C., 1976, J. Exp. Biol. 65:51-63) identified this as a K+ current. It was further found to be a calcium-activated K+ current since this increased outward K+ current cannot be elicited when the internal calcium is buffered with injected EGTA. The mutation pwB, which blocks the inward calcium current, also blocks this increased outward K+ current in teaA. This shows that this mutant current is activated by calcium through the normal depolarization-sensitive calcium channel. While tail current decay kinetic analysis showed that the apparent inactivation rates for this calcium-dependent K+ current are the same for mutant and wild type, the teaA current activates extremely rapidly. It is fully activated within 2 msec. This early activation of such a large outward current causes a characteristic reduction in the amplitude of the action potential of the teaA mutant. The teaA mutation had no effect on any of the other electrophysiological parameters examined. The phenotype of the teaA mutant is therefore a general decrease in responsiveness to depolarizing stimuli because of a rapidly activating calcium-dependent K+ current which prematurely repolarizes the action potential.

Animals↗