Two-dimensional agarose gel electrophoresis as a tool to isolate genus- and species-specific repetitive DNA sequences

Two-dimensional electrophoresis in agarose gels separates DNA-restriction fragments not only by molecular weight but also according to their AT-cluster content. The method produced genus-specific spot patterns of multicopy DNA fragments of grains as well as spot patterns of highly repetitive DNA fragments of ciliates, demonstrated for barley, spelt, and Tetrahymena. Further investigations in regard to their specificity by hybridization with three other grain species (wheat, oat, and rye) and three ciliate species (Tetrahymena thermophila, Tetrahymena pigmentosa, and Tetrahymena borealis) were performed. The DNA samples from spelt and Tetrahymena were demonstrated to be genus specific for Triticum and species specific for Tetrahymena pyriformis, respectively.

Characterization of DNA-directed RNA polymerases in isolated macronuclei of the ciliated protozoan Tetrahymena thermophila. Effects of purified ornithine decarboxylase and amine compounds

The possible regulatory interactions of purified ornithine decarboxylase with DNA-directed RNA polymerases in isolated macronuclei from the ciliated protozoan Tetrahymena thermophila were studied. It has been found that highly purified ODC (specific activity 10.2 mumols CO2 x h-1 x mg-1), even at activities of 37,500 nmol CO2 x h-1 per ml failed to alter RNA polymerase activity in the in vitro transcription assay in the presence or absence of the substrate L-ornithine at 20mM. The naturally occurring di- and polyamines putrescine, spermidine, and spermine stimulated in-vitro-transcription in isolated macronuclei more at optimal Mg2+/Mn(2+)-concentrations than at suboptimal concentrations, suggesting that polyamines act via a mechanism which is distinct from that of the inorganic cations. Of the monovalent amine compounds tested, (NH4)+ at high concentrations between 40 and 50mM slightly stimulated activity whereas the onset of stimulation by the organic amine compounds, piperidine and cyclohexylamine, was inversely related to the hydrophobicity of each particular compound. In the series of divalent amines, the correct distance between the N-atoms appeared to be very important since ethylenediamine and piperazine did not stimulate significantly but did inhibit at concentrations above 5 mM. 1,3-Diaminopropane stimulated slightly but inhibited above 10 mM, whereas the 1,4-diamino compounds putrescine and 1,4-diaminocyclohexane (DAC) were equally potent stimulators with the more hydrophobic one, DAC, reaching the maximum at lower concentrations than putrescine. For the trivalent amines, the influence of correct spacing seems not to be as important: N-(2-aminoethyl)piperazine stimulated very similar to spermidine.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of ornithine decarboxylase activity in the growth cycle of Tetrahymena thermophila

Cells of the ciliated protozoan Tetrahymena thermophila, grown in proteose peptone medium up to late logarithmic phase, harvested by centrifugation, and resuspended in fresh medium to almost the same cell density, underwent one more division cycle within 5 h after inoculation, thereafter being definitely in full stationary phase. This growth cycle proved to be a useful tool to investigate the activation and deactivation of ornithine decarboxylase ODC1 in Tetrahymena: In late logarithmic phase the cells contained a very low specific activity of ODC of about 3 nmol CO2.h-1.mg-1 in the soluble protein fraction. After growth stimulation the activity was increased up to 100-fold within 1 h. This high activity was maintained for about 5 h-about as long as division activity-then rapidly declined with a half life time (t1/2) of about 15 min to the original low level. Inhibition assays with cycloheximide and actinomycin D revealed that: i. the rapid increase of ODC activity was biphasic with one component of translation of preexisting mRNA and one component of translation of newly transcribed mRNA; ii. the t1/2 of the mRNA of ODC was estimated to be about 2 h; iii. inhibition of protein biosynthesis before ODC inactivation at 5 h caused a decrease of ODC with a t1/2 of 55 min instead of 15 min. These findings suggest that ODC activity in Tetrahymena is regulated on both levels: transcription and translation and by an inactivating protein factor which is regulated at the level of biosynthesis.

Properties of purified L-ornithine decarboxylase (EC 4.1.1.17) from Tetrahymena thermophila

Ornithine decarboxylase (ornithine carboxy lyase; EC 4.1.1.17) (ODC) from Tetrahymena thermophila was purified 6,300 fold employing fractionated ammonium sulfate precipitation, gel permeation chromatography on Sephadex G-150, ion exchange chromatography on DEAE-Sepharose CL-6B, and preparative isoelectric focussing. The product obtained in 24% yield was a preparation of the specific activity of 10,200 nmol CO2.h-1.mg-1. The purified enzyme was rather stable at 37 degrees C (14% loss of activity within 1 h). The molecular and catalytic properties of this enzyme were investigated. The isoelectric point was 5.7 and the molecular weight (MW) was estimated to be 68,000 under nondenaturing conditions. The pH optimum was between 6.0 and 7.0, the Km for the substrate L-ornithine was 0.11 mM, and the Km for the cofactor pyridoxal 5-phosphate was 0.12 microM; the product of ODC catalysis, putrescine, was a poor inhibitor with an estimated Ki of about 10 mM. The enzyme was inhibited competitively by D-ornithine with a Ki of 1.6 mM and by alpha-difluoromethylornithine with a Ki of 0.15 mM. The latter one, an enzyme activated irreversible inhibitor of mammalian ODC, inactivated the enzyme from T. thermophila at high concentrations with a half life time of 14 min. Other basic amino acids, e.g. L-lysine, L-arginine, and L-histidine, were neither substrates nor inhibitors of the enzyme, as were the diamines 1,3-diaminopropanol and cadaverine, the polyamines spermidine and spermine and the cosubstrate analogues pyridoxal and pyridoxamine-5-phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of L-arginine iminohydrolase (EC 3.5.3.6) from Tetrahymena thermophila by putrescine and spermidine: feedback control of polyamine biosynthesis

L-Arginine iminohydrolase (arginine deiminase, ADI) from Tetrahymena thermophila was purified approx. 75-fold by means of gel permeation chromatography. The Km of the purified enzyme for L-arginine was 412 +/- 25 microM and L-ornithine inhibited the reaction competitively with a Ki of 985 +/- 105 microM. D-Ornithine was a weak inhibitor with a Ki of greater than 10mM. The polyamines putrescine and spermidine inhibited ADI incompetitively with a Kii of 2.8mM for putrescine and 4.3mM for spermidine. Since the concentrations required for inhibition were within the range of the normal intracellular polyamine concentrations in Tetrahymena (maximally 14mM putrescine and 4mM spermidine), it is suggested that the polyamine effects on ADI are of regulatory nature. Thus, polyamine biosynthesis in Tetrahymena thermophila is regulated not only on the level of ornithine decarboxylase activity, but also on an earlier step, the supply of ODC with substrates.

Stimulation of growth and polyamine biosynthesis of the ciliated protozoan Tetrahymena thermophila. Regulation by L-arginine

Tetrahymena thermophila cells grown in a synthetic nutrient medium for 9 h removed 97% of the free L-arginine but less than 50% of any of the other essential amino acids. The major portion of the arginine was degraded rapidly (76-92%) whereas 5-15% was conserved as intact and only 2.5-10% were incorporated into protein. However, if bovine serum albumin (BSA) was present in the medium as a macromolecular arginine source the incorporation of free arginine into protein was reduced to less than 1% but the degraded fraction was increased. Apparently, the uptake mode of arginine determines its fate: arginine taken up by phagocytosis is bound for protein biosynthesis, arginine taken up by membrane receptors is chanelled to degradation. Media without arginine did not support growth of Tetrahymena. Citrulline and ornithine, the precursors of arginine biosynthesis in yeast and vertebrates, were not able to substitute for arginine. Pronounced morphological changes, e.g. greatly reduced ribosome content, were observed in Tetrahymena cells after 24 h of arginine starvation in otherwise complete medium, but not in cells starved in water, salt solution, or buffer. Thus, arginine is an essential nutrient component for Tetrahymena and the rapid degradation of this compound involving the enzymes arginine deiminase (ADI) and citrulline hydrolase (CH) might be of regulatory importance for the unicellular, as it is the case with acetylcholine and catecholamines in mammalian organisms. Since the product of these enzymes, L-ornithine, is the substrate for the regulatory key enzyme of polyamine biosynthesis, ornithine decarboxylase (ODC), the effects of the presence of absence of arginine on the activities of each particular enzyme of the pathway were studied, including ODC and the enzyme ornithine-oxo-acid aminotransferase (O delta T), which is a competitor of ODC for the common substrate. The arginine-degradative pathway was stimulated by extracellular free but not by peptide-bound arginine and was modulated by extracellular protein which induced phagocytosis; O delta T was stimulated with a time lag. The stimulation of ODC was in a reciprocal relation to the arginine concentration and enhanced by phagocytosis and previous arginine starvation.(ABSTRACT TRUNCATED AT 400 WORDS)

Polyamine effects on DNA-directed RNA polymerases in the ciliate Tetrahymena thermophila. In vivo- and in vitro-experiments suggesting highly specific regulative interactions

Stimulation of growth in resting cultures of the ciliated protozoan Tetrahymena thermophila stimulated putrescine formation in a manner coordinated to transcription and partly to DNA-polymerisation. The stimulation of polyamine biosynthesis involved increased formation of the precursor L-ornithine from L-arginine as well as stimulation of the regulative key enzyme ornithine decarboxylase. In order to characterize the interrelationships between polyamines and transcription, which were suggested by these in vivo-assays, in vitro-assays were performed employing isolated pure macronuclei from Tetrahymena thermophila. The results obtained were: i) The diamine putrescine and the polyamines spermidine and spermine stimulated the incorporation of [4-14C]UTP into RNA time- and concentration dependently. This stimulation was not due to changes in the ionic strength nor to substitution for divalent cations (e.g. Mg2+ or Mn2+). The di- and polyamines did not alter the Km of RNA polymerases for the substrates, e.g. UTP. ii) Purified yeast-RNA, when added to the in vitro transcription system at concentrations capable of stimulating purified ornithine decarboxylase from Tetrahymena inhibited the RNA polymerases. The inhibitory effect of RNA on the polymerases was partly antagonized by spermidine and spermine but not by putrescine whereas the residual polymerase activity was stimulated by all three bases. iii) The stimulating effects of the di- and polyamines were synergistic but not absolutely additive, suggesting different targets for their actions. iv) Stimulation of RNA polymerases by putrescine, spermidine, or spermine after inhibition of particular enzymes by alpha-amanitin allowed to distinguish the effects on the three polymerases (I, II, and III): putrescine was not specific for any of the polymerases; spermidine was most active stimulating polymerase I and spermine was most active stimulating polymerase II, less active stimulating polymerase I but strongly inhibitory to polymerase III. v) The results obtained in the previous experiments were confirmed by electrophoretic analysis of the products formed in the in vitro transcription assays which furthermore showed that the differences between the experiments with or without polyamines were most pronounced if partly denatured calf thymus DNA was present in the assay mixture. This finding and the inhibition by RNA suggest that the factor influenced most by the polyamines is the binding of the RNA polymerases to the DNA target.

Induced tubulin synthesis is caused by induced gene transcription in Tetrahymena

Tubulin synthesis and tubulin m RNA concentrations increase to variable extents during ciliary regeneration in the ciliate Tetrahymena. Experiments described here were carried out to determine whether the increased tubulin mRNA concentrations are due to induced transcription of tubulin genes or to stabilization of tubulin mRNA. In vivo labeling experiments with [3H]uridine and in vitro transcription assays suggest that under conditions of increased protein and tubulin synthesis the rate of transcription is enhanced. Hybridization assays of in vitro transcribed RNA also demonstrate qualitatively that the tubulin genes are transcribed at higher rates when tubulin synthesis is stimulated during ciliary regeneration. This observation is supported by measurements of the half-life of tubulin mRNA molecules in nondeciliated cells: This is approximately 2 h. Since the concentration of tubulin mRNA in cells engaged in cilia regeneration increases from 5 to 19-fold during the first hour of the regeneration period, even a complete stabilization of the tubulin mRNA molecules could not account for an increase in tubulin mRNA concentration of this magnitude.