Partial Reversion Research Articles

Effect of formalin toxoiding on Pseudomonas aeruginosa toxin A: biological, chemical, and immunochemical studies.

We investigated the effect of Formalin toxoiding on the biological, chemical, and immunological activities of Pseudomonas aeruginosa toxin A. Formalin treatment alone resulted in a 1,000-fold decrease in toxin-induced cell cytotoxicity and altered the antigenicity of the toxin A molecule without adversely affecting enzymatic activity. Competitive blocking experiments indicated that Formalin-mediated detoxification proceeded via alterations in a region of the toxin molecule other than the active site of the enzyme. The addition of lysine to Formalin-toxin mixtures not only increased the rate and extent of detoxification and antigenic alteration, but also completely destroyed enzymatic activity. The immunogenicities of different toxoids varied substantially. Upon dialysis and storage, Formalin-derived toxoids underwent partial toxic reversion, whereas a Formalin-lysine-derived toxoid did not. The sodium dodecyl sulfate-polyacrylamide gel patterns of Formalin- and Formalin-lysine-treated toxins indicated that these treatments caused the formation of a heterogenous group of high-molecular-weight species and produced substantial changes in the electrophoretic mobility of toxin A.

Effect of nuclear localization of large tumor antigen on growth potential of SV40-transformed cells

Transport-defective mutants of PARA, an SV40-adenovirus 7 hybrid virus, induce the synthesis of SV40 large T-antigen (T-ag) that is not transported to the nucleus and accumulates in the cytoplasm (cT-ag) of infected and transformed cells. The ability of cT mutants of PARA to induce phenotypic transformation of hamster embryo fibroblasts was examined. The cytoplasmic localization of T-ag was not stable, as extensive subculturing resulted in cell populations comprised of mixtures of cells which expressed T-ag in either the nucleus and/or the cytoplasm. Clonal analysis resulted in the selection of two cell populations: one cell type expressed T-ag solely in the cytoplasm and the second contained a mixture of cells which expressed T-ag in the nucleus and/or the cytoplasm. Serial subculture of clonal cell lines containing T-ag exclusively in the cytoplasm resulted again in the evolution of mixed populations which expressed T-ag in the nucleus and/or the cytoplasm. Analysis of synchronized cultures of such mixed clonal lines revealed that the intracellular distribution of T-ag was under the influence of the cell cycle; T-ag was present in the nucleus during S-phase, the period of maximal DNA synthesis, and in the cytoplasm during other phases of the cell cycle. These results suggest that a selective advantage exists during in vitro culturing for cells with a partial reversion of the cT phenotype. Examination of the growth properties of clonal lines in vitro indicated that cells in which T-ag could be detected in the cytoplasm, either continuously or during certain phases of the cell cycle, exhibited reduced growth potential under stringent culture conditions relative to wild-type transformants, behaving more like minimal transformants. In addition, the capacity for tumor induction in weanling hamsters by PARA(cT)-transformed hamster cells was reduced substantially in comparison to wild-type transformed cells. These results suggest that the constant presence of SV40 T-ag in the nucleus promotes maximal expression of the transformed cell phenotype.

Aberrant Forms of Streptococcus cremoris HP

The cheese starter strain, Streptococcus cremoris HP, produced variant colonies when streaked on the surface of solid media and incubated at 30 or 37 degrees C or in the presence of penicillin. Serial plating and incubation at 37 degrees C or in the presence of penicillin resulted in the production of variants. Subculture followed by incubation at 25 degrees C or in the absence of penicillin resulted in the reversion or partial reversion to the parent form. Colony morphology and cell morphology exhibited the characteristics of the L-phase. Evidence suggested that the aberrant forms of S. cremoris at 30 degrees C were transitional phase variants but at 37 degrees C and in the presence of penicillin they were L-phase variants. Electron micrographs showed that the cell walls of the variant cells were defective and that there were differences in the density and the organization of the cytoplasmic constituents compared with the parent cell.

Synaptic proteins after electroconvulsive stimulation: reversibility and regional differences in the brain.

The pattern of changes in brain-specific proteins mainly related to the synapses were studied in rats given electroconvulsive stimuli (ECS). One group was studied after three ECS per week for 4 weeks, another was further allowed a recovery period of 12 weeks. The experimental animals were compared with adequate controls. Brain-specific proteins were analyzed using crossed immunoelectrophoresis. The changes in the protein pattern after 4 weeks of ECS differed in the regions studied and are interpreted as follows: in the hypothalamus the amount of synapses seem to have increased, in the forebrain synaptic remodelling is under way and in the occipital cortex a delay in the neuronal development has been induced. The results further indicate an overall increased preparedness to meet the glycolytic demands accompanying seizure. Following 12 weeks of recovery a partial reversion of the induced changes was observed. The implication of the findings in relation to newer concepts of the working action of electroconvulsive therapy is discussed.

Dedifferentiated variants of a rat hepatoma: Partial reversion induced by cell aggregation

Dedifferentiated rat hepatoma variant cells of clone Faof1 fail to express most of the liver-specific functions characteristic of its line or origin, H4IIEC3. When Faof1 cells are cultivated for 48 hr in the form of aggregates two cell types can be recovered from monolayer cultures established from the aggregates: the majority of cells are similar to the Faof1 parental line, but a new cell type (designated dag) that adheres only weakly to the substrate is present at a frequency of 2–12 × 10 −2. Eight dag populations and eight clones are characterized as being different from Faof1 cells by the production of serum albumin, aldolase B and in some cases activity of alcohol dehydrogenase and alanine aminotransferase. No dag cells are recovered after 18 or 24 hours of aggregation, but after 48 or 96 hrs 1–5% of the cells give rise to clones of dag cells. During aggregation cells are committed to become dag cells but their new phenotype is expressed only after 5–12 days. The fraction of dag cells in colonies that grow out from aggregates suggests that dag transformation is not a clonal event. These experiments demonstrate that a transitory change in the culture conditions of Faof1 cells can lead to a heritable modification in phenotypic expression. Since dag cells fail to express the liver-specific gluconeogenic enzymes that permit cells to grow in glucose-free medium, it is possible to select from dag populations revertants in which expression of these activities is restored. The frequency of appearance of such dag revertants is not increased by the action of EMS.

Establishment of Escherichia coli cells with an integrated high copy number plasmid.

The dnaA46 cells can grow at high temperature when a high copy number plasmid pKY31, a derivative of pBR322 carrying a segment of the E. coli chromosome, integrates into the bacterial chromosome. In contrast, the dnaA46 polA- cells with the integrated plasmid can not grow at high temperature. Therefore, integration of the plasmid can suppress the dnaA mutation and this suppression requires DNA polymerase I which has been known to be required for plasmid replication. Full reversion of polA or lysogenization of λpolA+ is lethal for the dnaA46polA- bacteria that carry the plasmid only in integrated state. Partial reversion of polA allows these cells to grow at both low and high temperatures. Introduction of the plasmid pBR322 into cytoplasm of these bacteria suppresses the lethal effect caused by full reversion of polA or lysogenization of λpolA+. This lethal effect expresses independent of the presence or absence of the dnaA mutation. In partial revertants of polA which have only integrated plasmid, the number of copies of a region near the replication origin of integrated plasmid increases. The number is reduced by the presence of extrachromosomal pBR322. It is suggested that the lethal effect of normal levels of DNA polymerase I in strains that carry only the integrated plasmid is due to excessive initiation of replication of the bacterial chromosome from the plasmid origin and high potential of initiation can be absorbed in many copies of cytoplasmic plasmid, probably, in their replication origins.

Mechanism of enhanced precipitation phenomena in Pb(Sb) alloys with trace element As

The decomposition process of supersaturated solid solution of the Pb-Sb alloys with a small amount of As (∼0.01 wt pct), has been investigated by electrical resistivity measurement. The precipitation process of the Pb-Sb alloys with As is similar to that of the previously reported Pb-As alloys. In the first stage, diffusion of quenched-in excess vacancies accelerates and rate-controls the migration of As and Sb atoms forming an intermediate phase. The second stage is the precipitation of the intermediate phase under the equilibrium vacancy concentration and the third is precipitation of the equilibrium phase. A retardation of reaction in isothermal aging and a partial reversion in isochronal aging appear between the last two stages. The analysis of resistivity change in the Pb-As and Pb-Sb-As alloys shows that the composition and the crystal structure of the intermediate phase are different from those of the equilibrium phase. The mechanism that the preexisted intermediate phase acts as a preferential nucleation site for the equilibrium phase can explain the enhanced precipitation phenomena of the Pb-Sb alloys with trace element As. The reason for the difference in behavior between As and Sb atoms in lead is also discussed.

Partial reversal by fusicoccin of the inhibition imposed by abscisic acid on postgerminative growth of Halopappus gracilis

On the basis of the evidence that fusicoccin (FC) can reverse the inhibition of germination induced by abscisic acid (ABA) in Haplopappus gracilis seeds, but cannot restore normal postgerminative growth, we previously suggested that ABA may act through two different mechanisms, one involving H +/K + exchange at the plasmalemma level, the other interfering with nucleic acid and/or protein synthesis. In the present work we have analysed the interaction of FC with ABA concentrations lower than the 10 −5 M previously used. In these conditions, FC is able to induce a partial but significant reversion of the inhibition of DNA and chlorophyll synthesis and, in some cases, a nearly normal post-germinative growth. We are thus concerned with a system apparently inhibited not only at a membrane level that can, in some instances, be reversed by FC, which clearly acts only at the level of an H +/K + exchange mechanism operating on the plasmalemma. The possible interpretations are discussed.

Fungi as aids in higher plant classification

Host-parasite relationships and the uses of mycological data in plant classification are discussed. An important function of data from Uredinales is to indicate relative ages of origin for different groups of plants. When evolving rust lineages can be recognized they may provide detailed guidance on the direction of evolution. The available published and unpublished information in the field is reviewed. Rosaceae, Fabaceae, Onagraceae, Scrophulariaceae, Asteraceae, Poaceae, Cyperaceae, and Liliales are discussed in greatest detail. Some conclusions on relative ages in the monocotyledons are presented. It appears that Juncaceae must have been derived from Cyperaceae, by partial reversion to entomophily, rather than the reverse.

Suppression of a deletion mutation in the glutamine amidotransferase region of the Salmonella typhimurium trpD gene by mutations in pheA and tyrA

Prototrophic revertants of a trpD deletion mutant that lacks the glutamine amidotransferase domain of the bifunctional component II subunit of the anthranilate synthetase-phosphoribosyltransferase complex have been found to arise by the occurrence of sublethal missense mutations in either the pheA or tyrA loci. Such suppressor mutations were obtained directly by mutation of the wild-type pheA gene as well as indirectly by partial reversion of a variety of nonleaky pheA and tyrA mutations. The suppressor strains have only a portion of the normal level of the pheA or tyrA enzyme activity and thus experience a partial limitation in the synthesis of phenylalanine or tyrosine. This limitation leads to a relaxation of end-product regulation of the phenylalanine- or tyrosine-specific enzymes of the common aromatic pathway and to the overproduction of the branch point intermediate, chorismic acid, which is one of the substrates of the anthranilate synthetase reaction. It is proposed that the high intracellular level of chorismic acid acts to elevate the non-physiological NH3-dependent anthranilate synthetase activity of the component I subunit, thereby eliminating the need for the glutamine amidotransferase activity of the component II subunit. Consistent with this is the finding that phenylalanine and tyrosine are specific inhibitors of growth of the pheA and tyrA suppressor strains, respectively, causing a shutdown of the overproduction of chorismic acid by reestablishing normal end-product control of the common pathway.

Oak Seedlings Grown in Different Light Qualities

AbstractSeedlings of oak (Quercus robur) were germinated in darkness for 3 weeks and then given continuous light or short pulses of light (5–8 min every day). The morphological development was followed during 25 days. In continuous white, blue, and red light the stem growth terminated after about 10 days by formation of a resting bud. At that time the seedlings were about 100 mm high. In con tinuous long wavelength farred light (wavelength longer than 700 nm) the stem growth including leaf formation was continuous without the formation of resting buds, and the stem length was about 270 mm after 25 days. The number of nodes developed became twice that of the seedlings grown in while light. The leaves became well developed in all light colours, but leaf areas were largest in plants cultivated in white light. Compared to dark grown seedlings the mean area per leaf was increased about five times in continuous long wavelength far red light. A supplement with short (5 min) pulses of red light each day increased the leaf area up to 20 times.The stem elongation showed a high energy reaction response, i.e. the stem length increased only in continuous long wavelength far‐red light but was not influenced by short pulses of red light or far‐red light. The leaf expansion, however, was increased by short pulses of red light with a partial reversion of the effect by a subsequent pulse of far‐red light. The fraction of the plant covered with periderm was higher in plants given continuous light. In respect to periderm inhibition continuous long wavelength far red light was the most effective. The transfer of seedlings from darkness to continuous white light gave anthocyanin formation in the stem 10–20 mm below the apex. This formation took place in the cortex and was evident in plants grown in darkness or under short pulses of light. Plants grown in continuous red, blue or long wavelength Far red light showed only traces of anthocyanin.

Suppressor mutations causing partial reversion in the amiA region of Pneumococcus.

Mutants of an aminopterin-resistant strain of pneumococcus possessing four different suppressor genes have been isolated after mutagenesis with 5-BUdR. The suppressed strains exhibit a partial revertant phenotype since the parental aminopterin resistance remained unchanged but the associated sensitivity to an excess concentration of the branched chain amino acids L-isoleucine, L-valine and L-leucine was diminished almost to the level of the wild-type strain C13. The suppressor mutations had therefore dissociated the two properties associated with a mutation in the amiA cistron, namely aminopterin resistance and isoleucine sensitivity. The suppressor genes reduced the sensitivity to isoleucine of a number of amiA mutants, but had no effect on the level of resistance to a number of unrelated genes conferring resistance to other antibacterial substances. The suppressor mutations themselves did not confer resistance to aminopterin. Mapping of the suppressor mutations by recombination analysis and by clonal analysis showed them to be intragenic lying in the region near to the amiA-r19, amiA-r23, amiA-r17 loci.

Ａｌ‐Ｚｎ‐Ｍｇ合金溶接熱影響部の時効挙動

Hardness measurement, X-ray small angle scattering diffraction and transmission electron microscopy were carried out on the Al-4.5%Zn-1.2%Mg alloy welds. Dissolution, reversion, and partial reversion or coarsening of precipitates occur during welding in the heat-affected zones of the T4 and T6 treated materials. These structural changes depend on the peak temperature during welding or the distance from weld center. Softened zones are formed during post-weld aging at room temperature in the heat-affected region where partial reversion take place during welding. Softening in the heat-affected zones of these materials is attributed to differences in vacancy concentration, size distribution of precipitates and coarsening of precipitates.

Interaction of Ascorbate with the Radioprotective Effect of Mercaptoethylamin. An Exploratory Study in Mice, Whole Animals and Cell Cultures

The injection of ascrobate together with cysteamine (beta-mercaptoethylamin or MEA) was shown to cause a partial reversion of the radioprotective action of MEA in mice, and simultaneously of the suppressive action of MEA on RNA synthesis in bone marrow cells. In mouse spleen lymphocytes stimulated by concanavalin A in vitro, MEA and ascorbate exhibited a strong antagonism, neutralizing each other's inhibitory action on RNA synthesis. The latter effect failed to appear after chelation of trace metals, and it is indicated that the ability of ascorbate to counteract the effects of MEA on radiosensitivity and metabolism requires the formation of oxidized products, probably monodehydroascorbate, in agreement with previous observations on bacteria.

Ａｌ‐Ｚｎ‐Ｍｇ系合金溶接熱影響部の時効挙動に及ぼす合金組成の影響

Aging behaviors of the heat-affected zones in Al-24.5%Zn-1.24%Mg alloys welds were examined by means of hardness measurements and X-ray small angle scattering methods. The heat-affected zones in all the Al-Zn-Mg alloys welds are regions in the alloys which have been heated at 100°C or above by weld thermal cycles, where dissolution, reversion or partial reversion occurs. A re-solution treated or reverted area in the heat-affected zone is extended in the alloys containing more of Zn. Recovery rate of hardness in the heat-affected zone also increases with increase in Zn content except for the alloys containing small amounts of Mn, Cr, Zr, Cu and Fe. Softened areas are formed in the heat-affected zones of all the Al-Zn-Mg alloys welds during post-weld aging at room temperature. It is wider and remains longer in the Al-Zn-Mg alloys containing more of Mg.

Glycolysis mutants in Saccharomyces cerevisiae.

Mutants have been isolated in S. cerevisiae with the phenotype of growth on pyruvate but not on glucose, or growth on rich medium with pyruvate but inhibition by glucose. Screening of mutagenized cultures was either without an enrichment step, or after enrichment using the antibiotic netropsin (Young et al. 1976) or inositol starvation (Henry, Donahue and Culbertson 1975). One class of mutants lacked pyruvate kinase (pyk), another class had all the enzymes of glycolysis, and one mutant lacked phosphoglucose isomerase (pgi, Maitra 1971). Partial reversion of pyruvate kinase mutants on rich medium containing glucose gave double mutants now also lacking hexokinase (hxk), phosphofructokinase (fk), or several enzymes of glycolysis (gcr). In diploids the mutations were recessive. pyk, pgi, pfk, and gcr segregated 2:2 from their wild-type alleles. PYK hxk, PYK pfk, and PYK gcr segregrants grew on glucose.

Mutations in the L-arabinose operon of Escherichia coli B/r with reduced initiator function

Partial reversion mutants derived from a strain containing a strongly polar initiator-defective mutation (araI1036) in the L-arabinose operon were found to have several characteristics expected of mutants with reduced initiator function. These reversion mutations are cotransduced with the ara region and are probably within the araI region. Furthermore, they permit induction of the L-arabinose operon to a level only one-third of the normal wild-type level. These partially functional initiator regions reduce the expression of structural genes in the cis position only; they function quite independently of wild-type or defective initiator regions in the trans position. These mutants exhibit a two- to threefold increase in the rate of expression of ara operon genes within one-tenth of a generation after a shift of the growth temperature from 28 to 42 degrees C. This suggests that the temperature optimum for initiation of operon expression is higher for the partial revertant strains than it is for strains containing a wild-type initiator region.

Incorporation of triated leucine by axotomized rubral neurons

Fourteen kittens, 7–10 weeks of age, were injecteed with [ 3H]leucine 0.5–24 h before sacrifice 1–30 days after unilateral high cervical rubrospinal tractotomy. Histoautoradiographs of the red nuclei were prepared and counterstained with thionin. Axon reaction, evident histologically 24 h after surgery, was manifested by central chromatolysis or diffuse cytoplasmic chromophobia. Partial reversion toward a normal cytologic appearance was apparent 10–30 days postoperatively. Nucleolar and nuclear shrinkage and cytoplasmic atrophy were conspicuous accompaniments of axon reaction in rubral neurons. Expressed per cell the radioactivity of axotomized rubral nerve cells was consitently less than controls in animals surviving operation from 5 to 30 days. The data indicate that axon reaction in red nucleus is regressive in character and early associated with diminished protein synthesis. The frequently regressive nature of axon reaction in intrinsic neurons, such as those of red nucleus, probably is important in accounting for failure of regeneration of many mammalian CNS fiber tracts after injury.

Circadian rhythm in Schistosoma haematobium egg excretion

The usual peak daily egg excretion period in persons harbouring Schistosoma haematobium is the late morning and early afternoon. No evidence was found to support a hypothesis that the rhythm is mechanical in origin being due to rapid increase of bladder activity in the early morning. A partial reversion of the rhythm occurred when day shift workers changed to night shift. The possible role in the circadian rhythm of host factors—temperature and metabolism and of proteolytic enzyme secretion by miracidia are discussed.

Serum dependence of expression of the transformed phenotype: experiments with subline of mouse L fibroblasts adapted to growth in serum-free medium.

Characteristics of LSF cells grown in serum-containing and serum-free medium were compared. LSF is a subline of the L-strain of mouse transformed fibroblasts adapted to continuous growth is serum-free medium. Proliferation of LSF cells in monolayer on solid substratum was almost similar in serum-containing and in serum-free media. However, several other characters were found to be altered by the addition of serum to the serum-free medium: ability of cells to form colonies in semi-solid medium increased considerably; agglutinability of cells by Concanavalin A increased; uptake of 2-deoxy-D-glucose by the cells increased considerably; ability of cells to metabolize benzo (a) pyrene was inhibited; cell morphology was altered and, in particular, the cells became less spread on the substratum and density of microvilli on the cell surface increased. All these changes induced by serum were reversed by transfer of the cells back into serum-free medium. Thus, addition of serum increased the expression of a number of cellular traits characteristic of transformed phenotype, while in serum-free medium partial phenotypic reversion of transformation was observed. A possible role of serum in the expression of the transformed phenotype is discussed. It is pointed out that cell lines adapted to growth in serum-free medium provide an experimental system convenient for analysis of the effects of different serum components on the cell phenotype.