Characterization of the de novo pyrimidine biosynthetic pathway in Arabidopsis thaliana

We have characterized the enzyme cytidine deaminase. The full length cDNA was expressed in E. coli and purified to apparent homogeneity using a Ni-NTA agarose column. The Km and Vmax for cytidine were determined to be 226uM and 39.7 umoles/min respectively. The enzyme was also able to use 2\u27-deoxycytidine as substrate with an apparent Km of 49 uM and Vmax of 24 umoles/min.;We have also developed a single tube semi-quantitative relative reverse transcription polymerase chain reaction (RT-PCR) assay. We have used this assay to quantitate the relative transcript levels of the UMP synthase gene and the proximal SKIP5 F-box protein. We have determined that the two genes are coordinately transcriptionally up-regulated in Arabidopsis under conditions of pyrimidine starvation.;We have used our quantitative PCR method to analyze transcript levels of the entire de novo pathway of pyrimidine biosynthesis relative to the 18S rRNA. We have synthesized an oligonucleotide that is modified on its 3\u27 end and cannot be used by the polymerase in template extension. This attentuates the level of amplification of the 18S transcript. Under conditions of pyrimidine starvation ATCase and UMP synthase show the highest level of transcriptional up-regulation at 20 fold and 5 fold, respectively. During abiotic stress conditions of phosphate starvation, saline and flooding the pathway is relatively unaffected. Under completely anaerobic conditions DHOase, DHODH and UMP synthase transcript levels are severely reduced, while ATCase is unaffected. During ORMV infection DHODH and UMP synthase are both up-regulated by two and four fold, respectively.;We have generated lines of transgenic Arabidopsis plants containing the promoters of each member of the de novo biosynthetic pathway driving beta-glucuronidase expression. Two promoter GUS fusions were constructed for both ATCase and DHOase. The introns within the 5\u27 UTR of both these genes were required for expression within roots of our transgenic plants. Further, the DHOase intron is required for the highest levels of expression within aerial portions of the plants. The DHODH and UMP synthase promoters were both relatively weak in comparison to the ATCase and DHOase genes. Regions within the UMP synthase coding region conferred greatly increased GUS expression

Improved protocols for Aspergillus minimal medium: trace element and minimal medium salt stock solutions

Simplified protocols for ingredients of Aspergillus minimal medium (MM) are presented. These either do not change the final composition of MM or at most involve only minor modifications which, in extensive comparative tests, have not shown any effects on growth patterns of all strains/cultures tested

Cell adhesion and cortex contractility determine cell patterning in the Drosophila retina

Hayashi and Carthew (Nature 431 [2004], 647) have shown that the packing of cone cells in the Drosophila retina resembles soap bubble packing, and that changing E- and N-cadherin expression can change this packing, as well as cell shape. The analogy with bubbles suggests that cell packing is driven by surface minimization. We find that this assumption is insufficient to model the experimentally observed shapes and packing of the cells based on their cadherin expression. We then consider a model in which adhesion leads to a surface increase, balanced by cell cortex contraction. Using the experimentally observed distributions of E- and N-cadherin, we simulate the packing and cell shapes in the wildtype eye. Furthermore, by changing only the corresponding parameters, this model can describe the mutants with different numbers of cells, or changes in cadherin expression.Comment: revised manuscript; 8 pages, 6 figures; supplementary information not include

Measurement of Exclusive rho^0 rho^0 Production in Two-Photon Collisions at High Q^2 at LEP

Exclusive rho rho production in two-photon collisions involving a single highly virtual photon is studied with data collected at LEP at centre-of-mass energies 89GeV < \sqrt{s} < 209GeV with a total integrated luminosity of 854.7pb^-1 The cross section of the process gamma gamma^* -> rho rho is determined as a function of the photon virtuality, Q^2 and the two-photon centre-of-mass energy, Wgg, in the kinematic region: 1.2GeV^2 < Q^2 < 30GeV^2 and 1.1GeV < Wgg < 3GeV

Search for a Higgs Boson Decaying into Two Photons at LEP

A Higgs particle produced in association with a Z boson and decaying into two photons is searched for in the data collected by the L3 experiment at LEP. All possible decay modes of the Z boson are investigated. No signal is observed in 447.5 pb^-1 of data recorded at centre-of-mass energies up to 209 GeV. Limits on the branching fraction of the Higgs boson decay into two photons as a function of the Higgs mass are derived. A lower limit on the mass of a fermiophobic Higgs boson is set at 105.4 GeV at 95% confidence level

A search for W bb and W Higgs production in ppbar collisions at sqrt(s)=1.96 TeV

We present a search for W b \bar{b} production in p \bar{p} collisions at sqrt{s}=1.96 TeV in events containing one electron, an imbalance in transverse momentum, and two b-tagged jets. Using 174 pb-1 of integrated luminosity accumulated by the D0 experiment at the Fermilab Tevatron collider, and the standard-model description of such events, we set a 95% C.L. upper limit on W b \bar{b}$production of 6.6 pb for b quarks with transverse momenta p_T^b > 20 GeV and b \bar{b} separation in pseudorapidity-azimuth space Delta R_bb > 0.75. Restricting the search to optimized b \bar{b} mass intervals provides upper limits on$WH$production of 9.0$-$12.2 pb, for Higgs-boson masses of 105$-$135 GeV.Comment: 7 pages, 4 figures, 1 table, submitted to Physical Review Letter

Search for Heavy Isosinglet Neutrino in e+e- Annihilation at LEP

We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU(2)_L gauge group. The data collected with the L3 detector at center-of-mass energies between 130 GeV and 208 GeV are used.The decay channel N_e --> eW is investigated and no evidence is found for a heavy neutrino, N_e, in a mass range between 80 GeV and 205 GeV. Upper limits on the mixing parameter between the heavy and light neutrino are derived

Measurement of the Ratio of B+ and B0 Meson Lifetimes

The ratio of B+ and B0 meson lifetimes was measured using data collected in 2002-2004 by the D0 experiment in Run II of the Fermilab Tevatron Collider. These mesons were reconstructed in B -> mu+ nu D*- X decays, which are dominated by B0, and B ->mu+ nu D0bar X decays, which are dominated by B+. The ratio of lifetimes is measured to be t+/t0 = 1.080 +- 0.016(stat) +- 0.014(syst).Comment: 7 pages, 2 figures, LaTeX, to be submitted to Physical Review Letter

Search for right-handed W bosons in top quark decay

We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $\theta^*$ for each event. By comparing the $\cos\theta^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This measurement is consistent with the standard model prediction of f+=3.6x10^-4.Comment: Submitted to Physical Review D Rapid Communications 7 pages, 3 figure

Measurement of the Lifetime Difference in the B_s^0 System

We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/- 0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0) =1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width difference between the heavy and light mass eigenstates, Delta Gamma/Gamma = (Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst). With the additional constraint from the world average of the B_s^0$lifetime measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps and Delta Gamma/\Gamma = 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and B^0 lifetimes we obtain tau(B_s^0)/tau(B^0)} = 0.91 +/- 0.09 (stat) +/- 0.003 (syst).Comment: submitted to Phys. Rev. Lett. FERMILAB-PUB-05-324-