Nearest Neighbor Classification Rule for Mixtures of Discrete and Continuous Random Variables

In this paper very simple nonparametric classification rule for mixtures of discrete and continuous random variables is described. It is based on the method of nearest neighbor proposed by Cover and Hart (1967). The bounds on the limit of the nearest neighbor rule risks are given. Both lower and upper bound depend on the Bayes risk and the loss function. Finally the method is compared with other existing methods on some practical data set.     

Specificity of sterol-glucosylating enzymes from Sinapis alba and Physarum polycephalum.

1. Sinapis alba L. seedlings contain glycosyltransferase catalyzing the synthesis of sterol glucosides in the presence of UDPglucose as sugar donor. The major activity occurs in the membranous fraction sedimenting at 300--9000 x g. Successive treatment of the particulate enzyme fraction with acetone and Triton X-100 affords a soluble glucosyltransferase preparation which can be partly purified by gel filtration on Sephadex G-150. Molecular weight of the glucosyltransferase is 1.4 . 10(5). Apparent Km values for UDPglucose and sitosterol are 8.0 . 10(-5) M and 5.0 . 10(-6) M, respectively. 2. Comparison was made of the S. alba glucosyltransferase with a similar sterol-glucosylating enzyme isolated from non-photosynthesizing organism Physarum polycephalum (Myxomycetes). UDPglucose was the most efficient glucose donor in both cases but the enzyme from Ph. polycephalum can also utilize CDPglucose and TDPglucose. Glucose acceptors are, in case of both enzymes, sterols containing a beta-OH group at C-3 and a planar ring system (5 alpha-H or double bond at C-5). The number and position of double bonds in the ring system and in the side chain, as well as the presence of additional alkyl groups in the side chain at C-24 are of secondary importance. 3. The present results indicate that both enzymes can be regarded as specific UDPglucose:sterol glucosyltransferases. Certain differences in their specificity towards donors and acceptors of the glucosyl moiety suggest, however, a different structure of the active sites in both enzymes.     

DNA Repair and the Evolution of Transformation in Bacillus Subtilis. II. Role of Inducible Repair

In Bacillus subtilis, DNA repair and recombination are intimately associated with competence, the physiological state in which the bacterium can bind, take up and recombine exogenous DNA. Previously, we have shown that the homologous DNA transformation rate (ratio of transformants to total cells) increases with increasing UV dosage if cells are transformed after exposure to UV radiation (UV-DNA), whereas the transformation rate decreases if cells are transformed before exposure to UV (DNA-UV). In this report, by using different DNA repair-deficient mutants, we show that the greater increase in transformation rate in UV-DNA experiments than in DNA-UV experiments does not depend upon excision repair or inducible SOS-like repair, although certain quantitative aspects of the response do depend upon these repair systems. We also show that there is no increase in the transformation rate in a UV-DNA experiment when repair and recombination proficient cells are transformed with nonhomologous plasmid DNA, although the results in a DNA-UV experiment are essentially unchanged by using plasmid DNA. We have used din operon fusions as a sensitive means of assaying for the expression of genes under the control of the SOS-like regulon in both competent and noncompetent cell subpopulations as a consequence of competence development and our subsequent experimental treatments. Results indicate that the SOS-like system is induced in both competent and noncompetent subpopulations in our treatments and so should not be a major factor in the differential response in transformation rate observed in UV-DNA and DNA-UV treatments. These results provide further support to the hypothesis that the evolutionary function of competence is to bring DNA into the cell for use as template in the repair of DNA damage.     

Effects of UV-C radiation on extension growth, H+-extrusion and transmembrane electric potential in maize coleoptile segments

The effect of 253.7 nm ultraviolet radiation on elongation growth, medium acidification and changes in electric potential difference between vacuole and external medium in cells of maize ( Zea mays L.) coleoptile segments was investigated. It was found that irradiation with 390, 1170, 3900 and 5 850 J m⁻² UV-C (ultraviolet radiation 253.7 nm) inhibited elongation growth, whereas at 195 J m⁻² stimulation of growth was observed. The administration of IAA (10⁻⁵ M ) to the incubation medium of coleoptile segments partially abolished the inhibitory effect of UV-C. The pH of the incubation medium, measured simultaneously with growth, showed that the exposure of the segments to UV-C caused inhibition of H⁺-extrusion (or stimulation of H⁺ uptake). The presence of IAA (10⁻⁵ M ) in the incubation medium promoted (except after 5850 J m⁻² irradiation) H⁺-extrusion to a level comparable with that produced by IAA in non-irradiated segments. In UV-C irradiated segments the potential difference underwent significant alterations. Irradiation of coleoptile segments with 390 J m⁻² caused a transient depolarization, which was fully reversible within 30 min, while at higher doses depolarization was irreversible. The hyperpolarization of the membrane potential (MP) in cells of maize coleoptile induced by IAA was completely nullified by subsequent irradiation with UV-C. It is suggested that UV-C inhibited IAA-induced growth by a mechanism independent of cell wall acidification.     

The effect of yeast cell immobilization on the proportion of selected by-products of ethanol fermentation

Determination was made of the proportion of selected by-products (acetaldehyde, ethyl acetate, methanol, propanol, isobutanol, 2-methyl-butanol, 3-methyl-butanol) of batch and continuous ethanol fermentation carried out with the use of yeastSaccharomyces cerevisiae, strain 0–11, cells immobilized by adsorption on selected carriers (foamed polystyrene, bone shot, beech wood chips, porous glass) as well as by entrapping in calcium alginate and calcium pectinate gel.     

High Performance Liquid Chromatography of Molecular Species from Free Sterols and Sterylglycosides Isolated from Oat Leaves and Seeds

Free sterols and sterylglycosides (SG) from oat leaves and seedswere isolated by conventional thin layer chromatography (TLC)and subjected to high performance liquid chromatography (HPLC)for resolution of molecular species. Acylsterylglycosides, isolatedby TLC, were converted to SG by mild alkaline hydrolysis anddetermined as SG. Sterols and SG were injected onto the columnwithout any chemical treatment and the separated species weredetected at 200 nm. The separation of SG-species follows exactlythe separation of free sterols. Though gas liquid chromatography still is the method of choice,advantages of HPLC is to analyse directly the SG-species withouthydrolysis and derivatization as compared to GLC. After TLCthe sterol- and the SG-fraction are injected directly onto thecolumn. This is extremely important for labile sterylglycosidesor sterols, as demonstrated for the avenasterols. ¹ Preliminary reports have been presented on the "4. Arbeitstagung,Pflanzliche Lipide", October 7–8, 1983 in M?nster (FRG)and on the "6th International Symposium on the Structure, Functionand Metabolism of Plant Lipids", Neuchatel, Switzerland, July16–20, 1984. (Received November 12, 1984; Accepted January 14, 1985)     

Molecular cloning of a pea mRNA encoding an early light induced,nuclear coded chloroplast protein

Summary cDNA clones were isolated for a chloroplast protein, the mRNA of which is induced to maximum levels within 2–4 h after onset of illumination in five day old, etiolated pea seedlings. The cDNA library was constructed from poly(A)⁺-mRNA which was isolated from 4 h illuminated seedlings. The extremely short induction period of the early light induced protein(ELIP)-mRNA established the basis of our screening procedure. Colony hybridization experiments were performed with³²P-labelled cDNA probes, synthesized from RNA of seedlings which had been exposed to different programs of illumination. Plasmid DNAs were isolated from colonies showing strong hybridization signals exclusively with cDNA corresponding to the 4 h-mRNA. Hybrid released translation of preselected plasmids p 17/C2 and p17/C4 revealed a peptide of M_r 24 000. After posttranslational importin vitro, the processed product of M_r 17 000 appears in the chloroplast. Using these clones, the expression of the ELIP-mRNA was investigated by DOT-hybridization. The ELIP-mRNA reaches maximum levels within 2–4 hours after onset of illumination. Our results correspond precisely to thein vivo characteristics and indicate positive identification of the sought clones.     

DNA-dependent in vitro synthesis of enzymes of the galactose operon of Escherichia coli

Summary Two active enzymes of the galactose operon of Escherichia coli, uridyl transferase and galactokinase have been synthesized with high yields in a DNA dependent system for protein synthesis. The unspecific blank values amount to less than two percent of the rate obtained under optimal conditions and permit the accurate determination of even a small fraction of the maximum synthesis rate. Therefore this system provides a sensitive assay for the biological activity of DNA that contains the intact galactose operon of Escherichia coli.The synthesis of these galactose enzymes is to a high extent dependent on the presence of cyclic adenosine-3:5-monophosphate.D-fucose, known as an inducer of the galactose operon in vivo, stimulates the synthesis of galactokinase, indicating that the repressor of the galactose operon in active under these conditions. This stimulation is not observed, if the bacterial extract is prepared from a strain defective for the galactose repressor or if the DNA carries an operator constitutive mutation in the galactose operon. Therefore the stimulation by D-fucose is true derepression.