Ultrastructure and behaviour of the spindle pole body of the aphid-pathogenic fungusErynia neoaphidis

Summary A detailed account of the ultrastructure and behaviour of the spindle pole body (SPB) of the entomophthoraceous fungusErynia neoaphidis is presented for the first time.The SPB consists of extranuclear (ENC) and intranuclear (INC) components. The ENC is a saucepan-shaped structure which lies in a pocket of the nuclear envelope. It is composed of a forked, fibrillar handle and a shallow, cylindrical pan. The pan has a wall of two layers, both of which are thickened with a regular periodicity so that they appear to be beaded. It is postulated that the pan is formed from rough endoplasmic reticulum and that it synthesizes the amorphous, electron-dense material coating the ENC.The INC is a saucer-shaped, electron-dense plaque in which the ends of the spindle microtubules terminate. During metaphase, a clear zone separates the INC from the nuclear envelope and persists until telophase. The roles of the amorphous, electron-dense material and the clear zone as well as the method of SPB replication are discussed.     

Photoreversion und Photoprotektion bei UV-induzierten Mutationen des nichtphotoreaktivierbaren Bacteriums E.coli phr?

Summary Stationary phase cells of strain phr^–/MC 2 ofE. coli are not photoreactivable but the frequency of UV-induced mutations to low Streptomycine-resistance (S 3, 3/ml) is decreased strongly by illumination with light of fluorescence tubes (310 to 500 nm) after UV-irradiation. Also dark-reversion (DRM) of these mutations due to keeping UV-irradiated cells in saline is observed. Illumination before UV-irradiation decreases the frequency of the mutations (photoprotection against mutation=PPM) to the same extent as the combined action of photoreversion (PRM) and DRM. The lag-phase of cell division is prolonged strongly by illumination from 80 min without light to 150 min by the light-dose of highest activity. The additional lag is nearly the same if the illumination is done before, after or without UV-irradiation; this lag is about additive to the small lag caused by UV. Pre-illumination of the stationary-phase cells does not cause photoprotection against killing (PP), it even decreases the survival after high UV-doses. The observations support the hypothesis that PRM in this strain may be indirect, i.e. caused by the light-induced additional division lag which enhances the dark repair of UV-premutations. Also spontaneous premutations which are apparently present in the stationary-phase cells seem to be influenced by the light in this way.     

Theoretical studies on the necessary number of components in mixtures

Summary Theoretical studies on the necessary number of components in mixtures (for example multiclonal varieties or mixtures of lines) have been performed according to yielding ability. All theoretical investigations are based upon a Gram-Charlier frequency distribution of the component means with skewness ₁ and kurtosis ₂. The selected fraction p of the best components constitutes the mixture under consideration. The same selection differential S = S (p, ₁, ₂) can be realized by different parameter values of p, ₁ and ₂. Therefore, equal yield levels of the mixture can be achieved by different selected fractions p which implies different numbers of components in the mixture. Numerical results of S = S(p) for different values of ₁ and ₂ are presented and discussed. Of particular interest are the selected fractions p which lead to a maximal selection differential S. These results on S for large populations must be reduced in the case of finite population size. For this correction term we used an approximation B = B (p, n, ₁, ₂) given by Burrows (1972) where n = number of selected components. For given parameter values of ₁, ₂ and p, the necessary number n of components can be calculated by using the condition: Burrows-correction less than a certain percentage g of S — for example with g = 0.05 or g = 0.01. For given ₁ and ₂, the number n leading to a maximal selection differential S can be regarded as necessary number of components (necessary = maximum gain of selection under the given conditions). Numerical results are given for ₂ = 0 and for eight situations which are defined by linear relations ₂ = c ₁ between skewness and kurtosis. These cases will contain all possible numerical situations for ₁ and ₂, which may be relevant for practical applications. The necessary number of components turns out to be nearly independent of the numerical value of the kurtosis ₂. The n-intervals leading to selected fractions p from 0.01 to 0.20 approximately are: 2 n 4 for g = 0.05, 6 n 20 for g = 0.01 and 11 n 40 for g = 0.005, respectively. However, percentages g less than 0.01 would be unrealistically excessive. Therefore, following the assumptions and restrictions given in this paper one may conclude that n = 20 seems to be an appropriate upper bound for the necessary number of components in mixtures.     

Applications of cell culture for the improvement of human health

Current applications of Cell Culture Engineering which have a major beneficial impact for the improvement of human health range from a great variety of vaccines (examples include measles, mumps, rubella, polio, and Hepatitis A) made using this technology to a whole new range of therapeutic proteins dependent for their expression on animal cell culture hosts (examples include EPO, TPA and -interferon). Novel applications in the pipeline include cell therapy products and gene therapy products.     

Bias in genetic variance estimates due to spatial autocorrelation

Summary A central problem in the analysis of genetic field trials is the dichotomy of genetic and environmental effects because one cannot be defined without the other. Results from 768,000 simulated family trials in complete randomized block designs demonstrated a serious upward bias in estimates of family variance components from multi-unit plot designs when the phenotypic observations were compatible with a first-order autoregressive (AR1) process. The inflation of family variances and, thus, additive genetic variance and narrow sense individual heritabilities progressed exponentially with an increase in the nearest neighbor correlation () in the AR1 process. Significant differences in inflation rates persisted among various plot configurations. At = 0.2 the inflation of family variances reached 48–73%. Inflation rates were independent of the level of heritability. Modified Papadakis nearest neighbor (NN) adjustment procedures were tested for their ability to remove the bias in family variances. A NN-adjustment based on Mead's coefficient of interplant interaction and one derived from Bartlett's simultaneous autoregressive scheme removed up to 97% of the bias introduced by the phenotypic correlations. NN-adjusted estimates had slightly (5–8%) higher relative errors than did unadjusted estimates.     

Evolutionary origin of the class A and class C β-lactamases

Summary The protein sequences of 18 class A -lactamases and 2 class C -lactamases were analyzed to produce a rooted phylogenetic tree using the DD peptidase of Streptomyces R61 as an outgroup. This tree supports the penicillin-binding proteins as the most likely candidate for the ancestoral origin of the class A and class C -lactamases, these proteins diverging from a common evolutionary origin close to the DD peptidase. The actinomycetes are clearly shown as the origin of the class A -lactamases found in other non-actinomycete species. The tree also divides the -lactamases from the Streptomyces into two subgroups. One subgroup is closer to the DD peptidase root. The other Streptomyces subgroup shares a common branch point with the rest of the class A -lactamases, showing this subgroup as the origin of the non-actinomycete class A -lactamases. The non-actinomycete class A -lactamase phylogenetic tree suggests a spread of these -lactamases by horizontal transfer from the Streptomyces into the non-actinomycete gram-positive bacteria and thence into the gram-negative bacteria. The phylogenetic tree of the Streptomyces class A -lactamases supports the possibility that horizontal transfer of class A -lactamases occurred within the Streptomyces.     

Glucosylation of cyclodextrin-complexed podophyllotoxin by cell cultures of Linum flavum L.

The glucosylation of the cytotoxic lignan podophyllotoxin by cell cultures derived from Linum flavum was investigated. Four cyclodextrins: -cyclodextrin, -cyclodextrin, dimethyl--cyclodextrin and hydroxypropyl--cyclodextrin were used to improve the solubility of podophyllotoxin by complexation. Dimethyl--cyclodextrin met our needs the best and the solubility of podophyllotoxin could be enhanced from 0.15 to 1.92 mM, using a podophyllotoxin/cyclodextrin ratio of 1:1. Growth parameters of the cell suspensions were not affected neither by the addition of cyclodextrins alone, nor when complexed podophyllotoxin was dissolved in the medium.The complexed lignan disappeared rapidly from the culture medium, within 24h, under all experimental conditions. Almost simultaneously, between 73 and 100% of detectable podophyllotoxin was bioconverted into podophyllotoxin--d-glucoside. A maximal bioconversion rate of 0.51 mmol l^-1 suspension day^-1 was calculated for the L. flavum cells growing in a medium which included the podophyllotoxin/dimethyl--cyclodextrin complex at a final concentration of 1.35 mM.     

Influence of the size of inoculum on various growth phases inAspergillus oryzae

1) The duration of the lag phase of filamentous fungi should be expressed either as the time elapsing until exponential growth starts or until any growth takes place, but not until growth enters the linear phase or until mycelium formation is measurable.2) Exponential growth ofAspergillus oryzae can be established over a wide measurable range at a high rate of multiplication in vigorously aerated and agitated cultures where dispersed growth is obtained. Under such circumstances it is apparent that the rate of multiplication observed is equal to that in the non-measurable range which allows a determination of the lag phase with small inocula.3) The lag phase ofAspergillus oryzae is hardly affected by the size of the inoculum (conidia or mycelium) under various conditions of cultivation.4) Between inocula of 8 × 10⁷ and 4 × 10³ conidia per 100 ml and between 12.5 and 0.0008 mg mycelium per 100 ml the specific rate of growth in the exponential phase, and/or the rate of growth in the linear phase, and/or the maximum yield decreased with decreasing size of inoculum.5) The mentioned effects are dependent upon various factors. a) Trace elements markedly counteract the effects; however, the carry-over of these with large inocula is not sufficient to account for the observed phenomena. b) The higher the sugar concentration (at relatively low concentration of ammonium sulphate) the more pronounced are the effects, especially on maximum yield of mycelium. c) The effect on maximum yield is more pronounced if the cultures are strongly agitated and aerated. d) There is a tendency for early autolysis in the case of small inocula if the cultures are agitated (vibro mix and shaken cultures). e) Cultures originating from small inocula appear to be more easily influenced by the environment than cultures from large inocula in view of the larger variation of the results and the effects of products of heat sterilization where small inocula are used.6) Extremely large inocula (112 × 10⁷ and 288 × 10⁷ conidia per 100 ml) stimulate growth rate and maximum yield in substrates with 40 g/liter of maltose with or without trace elements. But at 80 g/liter of maltose a reversal of this effect is observed.7) Extremely small inocula (up to 20 reproductive units per 100 ml), in substrates poor in trace elements, can cause a marked increase in growth rate and maximum yield over those cultures originating from inocula 100 to 10,000 times larger.The experiments reported in this paper were carried out at the Department of Agricultural Bacteriology and Fermentation, Swiss Federal Institute of Technology, Zürich, Switzerland.     

Breeding systems and population structure in Limnanthes

Summary The breeding systems of seven Limanthes (Limanthaceae) populations, including one inbreeding and three outbreeding taxa, were quantified using a multilocus outcrossing rate estimator (t_m) and autofertility estimates. Along with the assays of heterozygosity levels, these data were used to separate components of effective outcrossing in terms of Wright's equilibrium inbreeding coefficient (F_e) and adult (F_A) and zygotic (F_Z) fixation indices. The patchy distribution of alleles as a potential source of substructure inbreeding was tested from the allelic frequencies mapped along a linear transect. Evidence for consanguineous matings in restricted neighborhoods and for selection at two different life cycle stages, and the efficiency of the protandrous breeding system were noted and discussed. Multilocus estimates of outcrossing are useful for their greater precision and unbiased nature while single locus estimates can help in detecting the effects of selection and population substructure. The data generally support the heterozygosity paradox noted by Brown (1979) but further suggest that the paradox may often result from a lack of precision of outcrossing estimates and from overlooking the stages of the life cycle being sampled.     

Ganglioside-cholera toxin interactions: a binding and lipid monolayer study

Summary On t.l.c. plates ¹²⁵I-cholera toxin binds to a disialoganglioside tentatively identified as GD_lb with about 10 times less capacity than to ganglioside GM₁. Binding of labeled toxin to both gangliosides was abolished in presence of excess amounts of unlabeled B subunit. Ganglioside extracts from human or pig intestinal mucosa showed toxin binding to gangliosides GM₁ and GD_1b. In ganglioside-containing lipid monolayers the penetration of the toxin was independent of the ganglioside binding capacity.Abbreviations GM₂ Gal-NAc14Gal(3-2NeuAc)14G1c1Cer - GM₁ Gal3Ga1-NAc14Gal(32NeuAc)14G1c11Cer - GD_1a NeuAc23Ga113Gal-NAc14Gal(32NeuAc)14G1c11Cer - GD1b Gall3Gal-NAcl4Gal(32NeuAc82NeuAc)14Glc11Cer - GT_1b NeuAc23Ga113Ga1-NAcal4Gal(3-2NeuAc82NeuAc)14G1c11Cer - dpPC 1,2-hexadecanoyl-sn-glycero-3-phosphocholine - dpPE 1,2-hexadecanoyl-sn-glycero-3-phosphoethanolamine     

Choosing category size in a stage projection matrix

Summary A basic problem associated with choosing category size in a stage projection matrix is described. Errors of estimation are large if the category size is chosen too small and errors of distribution are large if the category size is chosen too large. An approximate technique of balancing these two error types is suggested as a solution to this dilemma.     

Modelling inter-segmental coordination of neuronal oscillators: synaptic mechanisms for uni-directional coupling during swimming in Xenopus tadpoles

Locomotion requires longitudinal co-ordination. We have examined uni-directional synaptic coupling processes between two classes of neuronal network oscillators: autonomously active intrinsic oscillators, and potential oscillators that lack sufficient excitatory drive for autonomous activity. We model such oscillator networks in the bilaterally-symmetrical, Xenopus tadpole spinal cord circuits that co-ordinate swimming. Glutamate coupling EPSPs can entrain a second oscillator of lower frequency provided their strength is sufficient. Fast (AMPA) EPSPs advance spiking on each cycle, while slow (NMDA) EPSPs increase frequency over many cycles. EPSPs can also enable rhythmicity in potential oscillators and entrain them. IPSPs operate primarily on a cycle-by-cycle basis. They can advance or delay spiking to entrain a second intrinsic oscillator with higher, equal or lower frequency. Bilaterally symmetrical coupling connections operate twice per cycle: once in each half-cycle, on each side of the receiving oscillator. Excitatory and inhibitory coupling allow entrainment in complimentary areas of parameter space.     

Interaction of Topotecan,DNA Topoisomerase I Inhibitor,with Double-stranded Polydeoxyribonucleotides. 4. Topotecan Binds Preferably to the GC Base Pairs of DNA

Interaction of topotecan (TPT) with synthetic double-stranded polydeoxyribonucleotides has been studied in solutions of low ionic strength at pH 6.8 by linear flow dichroism (LD), circular dichroism (CD), UV-Vis absorption, and Raman spectroscopy. The complexes of TPT with poly(dG-dC)·poly(dG-dC), poly(dG)·poly(dC), poly(dA-dC)·poly(dG-dT), and poly(dA)·poly(dT), as well as complexes of TPT with calf thymus DNA and coliphage T4 DNA studied by us previously, have been shown to have negative LD in the long-wavelength absorption band of TPT, whereas the complex of TPT with poly(dA-dT)·poly(dA-dT) has positive LD in this absorption band of TPT. Thus, there are two different types of TPT complex with the polymers. TPT has been established to bind preferably to GC base pairs because its affinity to the polymers of different composition decreases in the following order: poly(dG-dC)·poly(dG-dC) > poly(dG)·poly(dC) > poly(dA-dC)·poly(dG-dT) > poly(dA)·poly(dT). The presence of DNA has been shown to shift the monomer–dimer equilibrium in TPT solutions toward dimer formation. Several duplexes of the synthetic polynucleotides bound together by bridges of TPT dimers may participate in the formation of the studied type of TPT–polynucleotide complex. Molecular models of TPT complex with linear and circular supercoiled DNAs and with deoxyguanosine have been considered. TPT (and presumably the whole camptothecin family) proved to represent a new class of DNA-specific ligands whose biological action is associated with formation of dimeric bridges between two DNA duplexes.     

Shared‐storage clusters

Clusters represent a collection of interconnected computers that collaborate on executing an application and present themselves as one unified computing resource. They are becoming an important segment in the computer industry. The two main flavors of cluster architectures are sharedstorage and sharednothing. This article presents host and I/O implementation details, and performance tradeoffs that need to be enforced due to sharing data in sharedstorage clusters. Sharing data requires the need for global concurrency and coherency protocols to maintain consistency of the database, and enforce data consistency in the local nodes buffers, respectively. Various sharedstorage architectures will be investigated, including the Virtual Shared and SharedIntermediate Memory models. This article also presents few selected sharedstorage clusters, including the DEC VAXCluster, IBM parallel Sysplex and Compaq/Tandem ServerNet.     

Concluding remarks

On the basis of symposium contributions onChlorella, Hibbertia, Eucalyptus, Ambrosia and on numerical approaches some fundamental problems of (bio)systematics, evolution, and taxonomic categories are discussed: Methods available for analysing affinities; conflicting evidence from phenetic, biochemical, cytogenetic and other analyses; further classification problems in cases of intermediacy, etc. While sibs of various levels and their natural hierarchy often can be objectively defined, this appears impossible for particular taxonomic levels itself (e. g. species). A single objective taxonomic system of organisms is unrealistic. Certain guiding lines for relative and practicable concepts of species and genus are proposed.Presented at the symposium Speciation and the Species Concept during the XIIth International Botanical Congress, Leningrad, July 8, 1975.     

“It Ain’t Over ‘til it’s Over”: Rethinking the Darwinian Revolution

This paper attempts a critical examination of scholarly understanding of the historical event referred to as the Darwinian Revolution. In particular, it concentrates on some of the major scholarly works that have appeared since the publication in 1979 of Michael Ruses The Darwinian Revolution: Nature Red in Tooth and Claw. The paper closes by arguing that fruitful critical perspectives on what counts as this event can be gained by locating it in a range of historiographic and disciplinary contexts that include the emergence of the discipline of evolutionary biology (following the evolutionary synthesis), the 1959 Darwin centenary, and the maturation of the discipline of the history of science. Broader perspectives on something called the Darwinian Revolution are called for that include recognizing that it does not map a one-to-one correspondence with the history of evolution, broadly construed.     

Feedback regulation of RNA polymerase subunit synthesis after the conditional overproduction of RNA polymerase in Escherichia coli

Summary The and subunit of RNA polymerase are thought to be controlled by a translational feedback mechanism regulated by the concentration of RNA polymerase holoenzyme. To study this regulation in vivo, an inducible RNA polymerase overproduction system was developed. This system utilizes plasmids from two incompatibility groups that carry RNA polymerase subunit genes under lac promoter/operator control. When the structural genes encoding the components of core RNA polymerase (, and ) or holoenzyme (, , and ⁷⁰) are present on the plasmids, induction of the lac promoter results in a two fold increase in the concentration of functional RNA polymerase. The induction of RNA polymerase overproduction is characterized by an initial large burst of synthesis followed by a gradual decrease as the concentration of RNA polymerase increases. Overproduction of RNA polymerase in a strain carrying an electrophoretic mobility mutation in the rpoB gene results in the specific repression of synthesis off the chromosome. These results indicate that RNA polymerase feedback regulation controls synthesis in vivo.     

A comparison and evaluation of some phytosociological techniques

Summary In three areas of vegetation (dune, mountain heath and salt marsh) the following phytosociological techniques have been tested and compared, using the same data: the Braun-Blanquet method; association and inverse analysis ofWilliams &Lambert; cluster analysis (agglomerative classification) based on different coefficients of similarity; and ordination (principal components analysis performed on matrices of different coefficients).The Braun-Blanquet method is considered to combine several advantages of the other methods and to be most economical in terms of efficiency (ratio of time input to information emerging).

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Zusammenfassung Auf drei verschiedenen Vegetationsflächen (Bergheide, Küstendünen und Salzwiesen) sind die folgenden pflanzensoziologischen Methoden geprüft und verglichen worden: die Methode von Braun-Blanquet; association analysis vonWilliams &Lambert (1959, 1961); Ordination (principal components analysis); und cluster analysis (Sokal &Sneath, 1963). Die letzteren beiden wurden mit verschiedenen Ähnlichkeitskoeffizienten geprüft.Auf Grund solchen Erfahrungen, zeigte sich die Braun-Blanquetische Methode leistungsfähiger als die anderen Methoden (d.h. optimale Einsicht in der Vegetation pro Arbeitsstunde). Sie vereinigte viele Vorteile der anderen Methoden.

     

Differential Expression and Association of Calcium Channel Subunits in Development and Disease

Voltage-gated calcium channels (VDCC) are essential to neuronal maturation and differentiation. It is believed that important signaling information is encoded by VDCC-mediated calcium influx that has both spatial and temporal components. VDCC are multimeric complexes comprised of a pore-forming ₁ subunit and auxiliary and ₂/ subunits. Changes in the fractional contribution of distinct calcium conductances to the total calcium current have been noted in developing and differentiating neurons. These changes are anticipated to reflect the differential expression and localization of the pore-forming ₁ subunits. However, as in vitro studies have established that regulates the channel properties and targeting of ₁, attention has been directed toward the developmental expression and assembly of isoforms. Recently, changes in the component of the omega-conotoxin GVIA (CTX)-sensitive N-type VDCC have indicated differential assembly of _1B with in postnatal rat brain. In addition, unique properties of 4 have been noted with respect to its temporal pattern of expression and incorporation into N-type VDCC complexes. Therefore, the expression and assembly of specific ₁/ complexes may reflect an elaborate cellular strategy for regulating VDCC diversity. The importance of these developmental findings is bolstered by a recent study which identified mutations in the 4 as the molecular defect in the mutant epileptic mouse (lethargic; lh/lh). As 4 is normally expressed in both forebrain and cerebellum, one may consider the impact of the loss of 4 upon VDCC assembly and activity. The importance of the lb and 4 isoforms to calcium channel maturation and assembly is discussed.