Deoxyuridine triphosphatase: A potential site of interaction with pyrimidine nucleotide analogues

Deoxyuridine triphosphatase has been purified from cultured human lymphoid cells in high yield and stable form by a relatively simple procedure. The properties differed somewhat from those reported previously, e.g. apparent K_m, molecular weight, and effects of divalent metals. No other naturally occurring dNTP or NTP serves as substrate, however, the enzyme may be an important site of interaction with intracellular derivatives of analogues of dUrd. It is shown here that deoxyuridine triphosphatase acts on araUTP, 6-azadUTP, 2′-FdUTP, and 2′,3′-dideoxyUTP, but the enzyme has no effect on 5-C1dUTP, 5-BrdUTP, 5-HgdUTP and dUrd-5′[α-thio]triphosphate. For the preparation of one of the analogues, the enzyme, trans-N-deoxyribosylase, from Lactobacillus, was used to prepare the deoxynucleoside from the base, a procedure that may have general usefulness.     

A rapid,single leaf,nucleic acid assay for determining the cytoplasmic organelle complement of rapeseed and related Brassica species

Summary An assay is described whereby Eco RI restriction fragment length polymorphisms of mitochondrial and chloroplast DNAs can definitively identify cytoplasms of interest in Brassica crop development. Restrictable mitochondrial and chloroplast DNA is extracted from as little as 2–3 g and 0.5 g leaf tissue, respectively, and the donor plants are able to continue to develop in a normal manner. An unknown cytoplasm can be identified in three days, which is a considerable saving in time and labor compared to the several years required by traditional methods. The assay is very inexpensive and should be established as a routine procedure in laboratories involved in sexual or somatic Brassica hybrid production.     

The Changing Shape of Plant Cells: Transformations During Cell Proliferation

Shapes of ideal cells can be inspected for the dynamic, or gnomonic,feature of producing daughter cells of the same shape. Suchfeatures can be found for (a) elongating epidermal cells, (b)isdiametrically enlarging epidermal cells, (c) elongating parenchymatouscells and (d) parenchymatous cells enlarging in three dimensions.Since each cell passes through a series of changes to finallyassume the form of the parental cell, a gnomonic cell must passthrough a gnomonic sequence of shapes during the cell cycle.A model tissue composed of gnomonic cells has complete stabilityof form through subsequent generations. Each of six parameters of ideal cells can be inspected in realcells in order to evaluate the effects of deviations from theideal on the stability of tissue pattern. (1) Cell plates ofreal and ideal cells do not expand for one generation. (2) Theangles in vertices of real cells shift over three cell cyclesfrom 170.1° to 137.3° to 124.0°, values close tothe expected set of 163°, 133° and 120° (3) Cellplates of real cells are not perpendicular to the longitudinalaxis of the cell. (4) Real cells do not divide synchronouslyas do ideal cells. (5) Real cells do not divide equally in halfas do ideal cells. (6) Finally, ideal cells have the same durationof the cell cycle whereas real cells have cycle times inverselyrelated to the initial size of the cell. It appears that a population of meristematic cells do not adhereto the restrictions of ideal cells, and consequently a significantamount of variance of form is added at each generation. Thereare two compensating mechanisms, one to hold size variationin check and one to keep shape deviations under control. Becauseof the probabilistic nature of cell division, cells increasein volume at various rates while the cell edges of all cellsexpand at a constant rate, indicating that the latter is theprimary element of growth while facet area and cell volume increasein dimension only for accommodation. Cell shape, gnomonic cells, Aponogeton elongatus, Lupinus alba     

Spin-label studies on phosphatidylcholine-cholesterol membranes: effects of alkyl chain length and unsaturation in the fluid phase

Dynamic properties of phosphatidylcholine-cholesterol membranes in the fluid phase and water accessibility to the membranes have been studied as a function of phospholipid alkyl chain length, saturation, mole fraction of cholesterol, and temperature by using spin and fluorescence labelling methods. The results are the following: (1) The effect of cholesterol on motional freedom of 5-doxyl stearic acid spin label (5-SASL) and 16-doxyl stearic acid spin label (16-SASL) in saturated phosphatidylcholine membrane is significantly larger than the effects of alkyl chain length and introduction of unsaturation in the alkyl chain. (2) Variation of alkyl chain length of saturated phospholipids does not alter the effects of cholesterol except in the case of dilauroylphosphatidylcholine, which possesses the shortest alkyl chains (12 carbons) used in this work. (3) Unsaturation of the alkyl chains greatly reduces the ordering effect of cholesterol at C-5 and C-16 positions although unsaturation alone gives only minor fluidizing effects. (4) Introduction of 30 mol% cholesterol to dimyristoylphosphatidylcholine membranes decreases the lateral diffusion constants of lipids by a factor of four, while it causes only a slight decrease of lateral diffusion in dioleoylphosphatidylcholine membranes. (5) If compared at the same temperature, 5-SASL mobilities plotted as a function of mole fraction of cholesterol in the fluid phases of dimyristoylphosphatidylcholine-, dipalmitoylphosphatidylcholine- and distearoylphosphatidylcholine-cholesterol membranes are similar in wide ranges of temperature (45-82 degrees C) and cholesterol mole fraction (0-50%). (6) In isothermal experiments with saturated phosphatidylcholine membranes, 5-SASL is maximally immobilized at the phase boundary between Regions I and III reported by other workers (Recktenwald, D.J. and McConnell, H.M. (1981) Biochemistry 20, 4505-4510) and becomes more mobile away from the boundary in Regions I and III. (7) 5-SASL in unsaturated phosphatidylcholine membranes showed a gradual monotonic immobilization with increase of cholesterol mole fraction without showing any maximum in the range of cholesterol fractions studied. (8) By rigorously determining rigid-limit magnetic parameters of cholestane spin labels in membranes from Q-band second-derivative ESR spectra to monitor the dielectric environment around the nitroxide radical, it is concluded that cholesterol incorporation increases water accessibility in the hydrophilic loci of the membrane. In contrast, 12-(9-anthroyloxy)stearic acid fluorescence showed that water accessibility is decreased in the hydrophobic loci of the membrane.     

Effect of iodide on estrogen-induced uterine peroxidase

Iodide administered in the drinking water for 5–7 days increased the activity of estradiol-induced uterine peroxidase in the immature rat. This effect was specific for iodide and could not be mimicked by chloride, bromide, thiocyanate, perchlorate or iodate. Sodium iodide also increased peroxidase activity in the parotid gland but had no effect on glucose-6-phosphate dehydrogenase in the uterus, thyroid or parotid even though estradiol produced a 2-fold increase in the activity of this enzyme in the uterus. ¹²⁵I was taken up more readily by the uterus than by muscle but this process was not influenced by prior treatment of the animals with estrogen. The in vitro effect of sulfhydryl reagents on uterine peroxidase was also investigated and proposals made for possible mechanisms of action of iodide on this enzyme in the intact animal.     

UDP-glucose: Indoleacetic acid glucosyl transferase and indoleacetyl-glucose: Myo-inositol indoleacetyl transferase

We have demonstrated the in vitro enzymatic synthesis of an ester of indole-3-acetic acid (IAA) and glucose and of IAA and myo-inositol by the following reaction sequence: lt]o| li]1) IAA + UDPG ? IAA-glucose +UDP li]2) IAA-glucose +myo-inositol → IAA-itmyo-inositol +glucose The enzymes were partially purified from extracts of immature kernels of Zea mays sweet corn and the two activities separated on a Sephadex G-150 column. Products were characterized, primarily, by comparison of their 70 eV mass spectra with those of authentic synthetic standards. To our knowledge this is the first example of enzymatically catalyzed acylation by a 1-O-acylsugar.     

Variability and genetics of spacer DNA sequences between the ribosomal-RNA genes of hexaploid wheat (Triticum aestivum)

Summary Using restriction enzyme digests of genomic DNA extracted from the leaves of 25 hexaploid wheat (Triticum aestivum L. em. Thell.) cultivars and their hybrids, restriction fragment length polymorphisms of the spacer DNA which separates the ribosomal-RNA genes have been examined. (From one to three thousand of these genes are borne on chromosomes 1B and 6B of hexaploid wheat). The data show that there are three distinct alleles of the 1B locus, designated Nor-B1a, Nor-B1b, and Nor-B1c, and at least five allelic variants of the 6B locus, designated Nor-B2a, Nor-B2b, Nor-B2c, Nor-B2d, and Nor-B2e. A further, previously reported allele on 6B has been named Nor-B2f. Chromosome 5D has only one allelic variant, Nor-D3. Whereas the major spacer variants of the 1B alleles apparently differ by the loss or gain of one or two of the 133 bp sub-repeat units within the spacer DNA, the 6B allelic variants show major differences in their compositions and lengths. This may be related to the greater number of rDNA repeat units at this locus. The practical implications of these differences and their application to wheat breeding are discussed.     

Character displacement in the fighting colours of Hetaerina damselflies

Aggression between species is a seldom-considered but potentially widespread mechanism of character displacement in secondary sexual characters. Based on previous research showing that similarity in wing coloration directly influences interspecific territorial aggression in Hetaerina damselflies, we predicted that wing coloration would show a pattern of character displacement (divergence in sympatry). A geographical survey of four Hetaerina damselfly species in Mexico and Texas showed evidence for character displacement in both species pairs that regularly occurs sympatrically. Hetaerina titia, a species that typically has large black wing spots and small red wing spots, shifted to having even larger black spots and smaller red wing spots at sites where a congener with large red wing spots is numerically dominant (Hetaerina americana or Hetaerina occisa). Hetaerina americana showed the reverse pattern, shifting towards larger red wing spots where H. titia is numerically dominant. This pattern is consistent with the process of agonistic character displacement, but the ontogenetic basis of the shift remains to be demonstrated.     

Zearalenone induces chromosome aberrations in mouse bone marrow: preventive effect of 17β-estradiol, progesterone and Vitamin E

The cytogenetic effect of zearalenone (ZEN), a non-steroidal estrogenic mycotoxin, was evaluated in vivo, in mouse bone marrow cells, by assessing the percentage of cells bearing different chromosome aberrations. The studies included different conditions for animal treatment, as follows: (1) single intraperitoneal (ip) injection, (2) repeated ip injections, (3) pre-treatment for 24 h with Vitamin E (Vit E), and (4) pre-treatment for 4 h with 17β-estradiol (17β-Est) or progesterone (Prog). ZEN induced different types of chromosome aberrations, which was concentration-dependent (2–20 mg/kg bw). These doses corresponded to 0.4–4% of the LD₅₀ in the mouse. Interestingly, when the dose of ZEN (40 mg/kg) was fractionated into four equivalent doses (4 × 10 mg/kg bw), into three doses (15 + 10 + 15 mg/kg bw), or into two equivalent doses (2 × 20 mg/kg bw), given every 24 h, the percentage of chromosome aberrations increased significantly. This finding suggests that ZEN proceeds by reversible binding on receptors that could become saturated, and that it damages the chromosomes in a ‘hit and go’ manner. Furthermore, pre-treatment of animals with 17β-estradiol or progesterone significantly decreased the percentage of chromosome aberrations, suggesting that (i) these hormones bind to the same cytoplasmic receptors transported into the nucleus to elicit DNA damage, (ii) they may play a role in preventing chromosome aberrations induced by ZEN. Similarly, Vit E prevented these chromosome aberrations indicating that Vit E, previously reported to prevent most of the toxic effects induced by ZEN, may also bind to the same receptors.