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We propose a quadrupolar exchange-only spin qubit that is highly robust against charge noise and nuclear spin dephasing, the dominant decoherence mechanisms in quantum dots. The qubit consists of four electrons trapped in three quantum dots, and operates in a decoherence-free subspace to mitigate dephasing due to nuclear spins. To reduce sensitivity to charge noise, the qubit can be completely operated at an extended charge noise sweet spot that is first-order insensitive to electrical fluctuations. Because of on-site exchange mediated by the Coulomb interaction, the qubit energy splitting is electrically controllable and can amount to several GHz even in the "off" configuration, making it compatible with conventional microwave cavities.

Electron spins in silicon quantum dots are attractive systems for quantum computing owing to their long coherence times and the promise of rapid scaling of the number of dots in a system using semiconductor fabrication techniques. Although nearest-neighbour exchange coupling of two spins has been demonstrated, the interaction of spins via microwave-frequency photons could enable long-distance spin-spin coupling and connections between arbitrary pairs of qubits ('all-to-all' connectivity) in a spin-based quantum processor. Realizing coherent spin-photon coupling is challenging because of the small magnetic-dipole moment of a single spin, which limits magnetic-dipole coupling rates to less than 1 kilohertz. Here we demonstrate strong coupling between a single spin in silicon and a single microwave-frequency photon, with spin-photon coupling rates of more than 10 megahertz. The mechanism that enables the coherent spin-photon interactions is based on spin-charge hybridization in the presence of a magnetic-field gradient. In addition to spin-photon coupling, we demonstrate coherent control and dispersive readout of a single spin. These results open up a direct path to entangling single spins using microwave-frequency photons.

We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a single electron that is dipole coupled to microwave photons in a superconducting cavity. Measurements of the cavity transmission reveal dispersive features due to the DQD valley states in Si. The occupation of the valley states can be increased by raising the temperature or applying a finite source-drain bias across the DQD, resulting in an increased signal. Using the cavity input-output theory and a four-level model of the DQD, it is possible to efficiently extract valley splittings and the inter- and intravalley tunnel couplings.

Although geometric phases in quantum evolution are historically overlooked, their active control now stimulates strategies for constructing robust quantum technologies. Here, we demonstrate arbitrary single-qubit holonomic gates from a single cycle of nonadiabatic evolution, eliminating the need to concatenate two separate cycles. Our method varies the amplitude, phase, and detuning of a two-tone optical field to control the non-Abelian geometric phase acquired by a nitrogen-vacancy center in diamond over a coherent excitation cycle. We demonstrate the enhanced robustness of detuned gates to excited-state decoherence and provide insights for optimizing fast holonomic control in dissipative quantum systems.

The goal of this article is to review the progress of three-electron spin qubits from their inception to the state of the art. We direct the main focus towards the exchange-only qubit (Bacon et al 2000 Phys. Rev. Lett. 85 1758-61, DiVincenzo et al 2000 Nature 408 339) and its derived versions, e.g. the resonant exchange (RX) qubit, but we also discuss other qubit implementations using three electron spins. For each three-spin qubit we describe the qubit model, the envisioned physical realization, the implementations of single-qubit operations, as well as the read-out and initialization schemes. Two-qubit gates and decoherence properties are discussed for the RX qubit and the exchange-only qubit, thereby completing the list of requirements for quantum computation for a viable candidate qubit implementation. We start by describing the full system of three electrons in a triple quantum dot, then discuss the charge-stability diagram, restricting ourselves to the relevant subsystem, introduce the qubit states, and discuss important transitions to other charge states (Russ et al 2016 Phys. Rev. B 94 165411). Introducing the various qubit implementations, we begin with the exchange-only qubit (DiVincenzo et al 2000 Nature 408 339, Laird et al 2010 Phys. Rev. B 82 075403), followed by the RX qubit (Medford et al 2013 Phys. Rev. Lett. 111 050501, Taylor et al 2013 Phys. Rev. Lett. 111 050502), the spin-charge qubit (Kyriakidis and Burkard 2007 Phys. Rev. B 75 115324), and the hybrid qubit (Shi et al 2012 Phys. Rev. Lett. 108 140503, Koh et al 2012 Phys. Rev. Lett. 109 250503, Cao et al 2016 Phys. Rev. Lett. 116 086801, Thorgrimsson et al 2016 arXiv:1611.04945). The main focus will be on the exchange-only qubit and its modification, the RX qubit, whose single-qubit operations are realized by driving the qubit at its resonant frequency in the microwave range similar to electron spin resonance. Two different types of two-qubit operations are presented for the exchange-only qubits which can be divided into short-ranged and long-ranged interactions. Both of these interaction types are expected to be necessary in a large-scale quantum computer. The short-ranged interactions use the exchange coupling by placing qubits next to each other and applying exchange-pulses (DiVincenzo et al 2000 Nature 408 339, Fong and Wandzura 2011 Quantum Inf. Comput. 11 1003, Setiawan et al 2014 Phys. Rev. B 89 085314, Zeuch et al 2014 Phys. Rev. B 90 045306, Doherty and Wardrop 2013 Phys. Rev. Lett. 111 050503, Shim and Tahan 2016 Phys. Rev. B 93 121410), while the long-ranged interactions use the photons of a superconducting microwave cavity as a mediator in order to couple two qubits over long distances (Russ and Burkard 2015 Phys. Rev. B 92 205412, Srinivasa et al 2016 Phys. Rev. B 94 205421). The nature of the three-electron qubit states each having the same total spin and total spin in z-direction (same Zeeman energy) provides a natural protection against several sources of noise (DiVincenzo et al 2000 Nature 408 339, Taylor et al 2013 Phys. Rev. Lett. 111 050502, Kempe et al 2001 Phys. Rev. A 63 042307, Russ and Burkard 2015 Phys. Rev. B 91 235411). The price to pay for this advantage is an increase in gate complexity. We also take into account the decoherence of the qubit through the influence of magnetic noise (Ladd 2012 Phys. Rev. B 86 125408, Mehl and DiVincenzo 2013 Phys. Rev. B 87 195309, Hung et al 2014 Phys. Rev. B 90 045308), in particular dephasing due to the presence of nuclear spins, as well as dephasing due to charge noise (Medford et al 2013 Phys. Rev. Lett. 111 050501, Taylor et al 2013 Phys. Rev. Lett. 111 050502, Shim and Tahan 2016 Phys. Rev. B 93 121410, Russ and Burkard 2015 Phys. Rev. B 91 235411, Fei et al 2015 Phys. Rev. B 91 205434), fluctuations of the energy levels on each dot due to noisy gate voltages or the environment. Several techniques are discussed which partly decouple the qubit from magnetic noise (Setiawan et al 2014 Phys. Rev. B 89 085314, West and Fong 2012 New J. Phys. 14 083002, Rohling and Burkard 2016 Phys. Rev. B 93 205434) while for charge noise it is shown that it is favorable to operate the qubit on the so-called '(double) sweet spots' (Taylor et al 2013 Phys. Rev. Lett. 111 050502, Shim and Tahan 2016 Phys. Rev. B 93 121410, Russ and Burkard 2015 Phys. Rev. B 91 235411, Fei et al 2015 Phys. Rev. B 91 205434, Malinowski et al 2017 arXiv: 1704.01298), which are least susceptible to noise, thus providing a longer lifetime of the qubit.

Gene function studies in Trypanosoma cruzi, the protozoan parasite that causes Chagas disease, have been hindered by the lack of efficient genetic manipulation protocols. In most organisms, insertion and deletion of DNA fragments in the genome are dependent on the generation of double-stranded DNA break (DSB) and repair. By inducing a site-specific DSB, zinc finger nucleases (ZFNs) have proven to be useful to enhance gene editing in many cell types. Using a pair of ZFNs targeted to the T. cruzi gp72 gene, we were able to generate gp72 knockout parasites with improved efficiency compared to the conventional gene knockout protocol. We also provide evidence that, in T. cruzi, repair of DSBs generated by ZFNs occurs primarily by the homologous recombination pathway., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Human African trypanosomiasis (sleeping sickness) is a neglected tropical disease caused by Trypanosoma brucei spp. The parasites are transmitted by tsetse flies and adapt to their different hosts and environments by undergoing a series of developmental changes. During differentiation, the trypanosome alters its protein coat. Bloodstream form trypanosomes in humans have a coat of variant surface glycoprotein (VSG) that shields them from the immune system. The procyclic form, the first life-cycle stage to develop in the tsetse fly, replaces the VSG coat by procyclins; these proteins do not protect the parasite from lysis by serum components. Our study exploits the parasite-specific process of differentiation from bloodstream to procyclic forms to screen for potential drug candidates. Using transgenic trypanosomes with a reporter gene in a procyclin locus, we established a whole-cell assay for differentiation in a medium-throughput format. We screened 7,495 drug-like compounds and identified 28 hits that induced expression of the reporter and loss of VSG at concentrations in the low micromolar range. Small molecules that induce differentiation to procyclic forms could facilitate studies on the regulation of differentiation as well as serving as scaffolds for medicinal chemistry for new treatments for sleeping sickness.

Elucidating the mechanism of action of trypanocidal compounds is an important step in the development of more efficient drugs against Trypanosoma brucei. In a screening approach using an RNAi library in T. brucei bloodstream forms, we identified a member of the mitochondrial carrier family, TbMCP14, as a prime candidate mediating the action of a group of anti-parasitic choline analogs. Depletion of TbMCP14 by inducible RNAi in both bloodstream and procyclic forms increased resistance of parasites towards the compounds by 7-fold and 3-fold, respectively, compared to uninduced cells. In addition, down-regulation of TbMCP14 protected bloodstream form mitochondria from a drug-induced decrease in mitochondrial membrane potential. Conversely, over-expression of the carrier in procyclic forms increased parasite susceptibility more than 13-fold. Metabolomic analyses of parasites over-expressing TbMCP14 showed increased levels of the proline metabolite, pyrroline-5-carboxylate, suggesting a possible involvement of TbMCP14 in energy production. The generation of TbMCP14 knock-out parasites showed that the carrier is not essential for survival of T. brucei bloodstream forms, but reduced parasite proliferation under standard culture conditions. In contrast, depletion of TbMCP14 in procyclic forms resulted in growth arrest, followed by parasite death. The time point at which parasite proliferation stopped was dependent on the major energy source, i.e. glucose versus proline, in the culture medium. Together with our findings that proline-dependent ATP production in crude mitochondria from TbMCP14-depleted trypanosomes was reduced compared to control mitochondria, the study demonstrates that TbMCP14 is involved in energy production in T. brucei. Since TbMCP14 belongs to a trypanosomatid-specific clade of mitochondrial carrier family proteins showing very poor similarity to mitochondrial carriers of mammals, it may represent an interesting target for drug action or targeting.

Normal human serum (NHS) confers human resistance to infection by the parasite Trypanosoma brucei owing to the trypanolytic activity of apolipoprotein L1 (APOL1), present in two serum complexes termed Trypanolytic Factors (TLF-1 and -2). In order to identify parasite components involved in the intracellular trafficking and activity of TLFs, an inducible RNA interference (RNAi) genomic DNA library constructed in bloodstream form T. brucei was subjected to RNAi induction and selection for resistant parasites under NHS conditions favouring either TLF-1 or TLF-2 uptake. While TLF-1 conditions readily selected the haptoglobin-haemoglobin (HP-HB) surface receptor TbHpHbR as expected, given its known ability to bind TLF-1, under TLF-2 conditions no specific receptor for TLF-2 was identified. Instead, the screen allowed the identification of five distinct factors expected to be involved in the assembly of the vacuolar proton pump V-ATPase and consecutive endosomal acidification. These data confirm that lowering the pH during endocytosis is required for APOL1 toxic activity., (© 2014 John Wiley & Sons Ltd.)

The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

Atom-scale defects in semiconductors are promising building blocks for quantum devices, but our understanding of their material-dependent electronic structure, optical interactions, and dissipation mechanisms is lacking. Using picosecond resonant pulses of light, we study the coherent orbital and spin dynamics of a single nitrogen-vacancy center in diamond over time scales spanning six orders of magnitude. We develop a time-domain quantum tomography technique to precisely map the defect's excited-state Hamiltonian and exploit the excited-state dynamics to control its ground-state spin with optical pulses alone. These techniques generalize to other optically addressable nanoscale spin systems and serve as powerful tools to characterize and control spin qubits for future applications in quantum technology., (Copyright © 2014, American Association for the Advancement of Science.)

The study of individual quantum systems in solids, for use as quantum bits (qubits) and probes of decoherence, requires protocols for their initialization, unitary manipulation, and readout. In many solid-state quantum systems, these operations rely on disparate techniques that can vary widely depending on the particular qubit structure. One such qubit, the nitrogen-vacancy (NV) center spin in diamond, can be initialized and read out through its special spin-selective intersystem crossing, while microwave electron spin resonance techniques provide unitary spin rotations. Instead, we demonstrate an alternative, fully optical approach to these control protocols in an NV center that does not rely on its intersystem crossing. By tuning an NV center to an excited-state spin anticrossing at cryogenic temperatures, we use coherent population trapping and stimulated Raman techniques to realize initialization, readout, and unitary manipulation of a single spin. Each of these techniques can be performed directly along any arbitrarily chosen quantum basis, removing the need for extra control steps to map the spin to and from a preferred basis. Combining these protocols, we perform measurements of the NV center's spin coherence, a demonstration of this full optical control. Consisting solely of optical pulses, these techniques enable control within a smaller footprint and within photonic networks. Likewise, this unified approach obviates the need for both electron spin resonance manipulation and spin addressability through the intersystem crossing. This method could therefore be applied to a wide range of potential solid-state qubits, including those which currently lack a means to be addressed.

Different life-cycle stages of Trypanosoma brucei are characterized by stage-specific glycoprotein coats. GPEET procyclin, the major surface protein of early procyclic (insect midgut) forms, is transcribed in the nucleolus by RNA polymerase I as part of a polycistronic precursor that is processed to monocistronic mRNAs. In culture, when differentiation to late procyclic forms is triggered by removal of glycerol, the precursor is still transcribed, but accumulation of GPEET mRNA is prevented by a glycerol-responsive element in the 3' UTR. A genome-wide RNAi screen for persistent expression of GPEET in glycerol-free medium identified a novel protein, NRG1 (Nucleolar Regulator of GPEET 1), as a negative regulator. NRG1 associates with GPEET mRNA and with several nucleolar proteins. These include two PUF proteins, TbPUF7 and TbPUF10, and BOP1, a protein required for rRNA processing in other organisms. RNAi against each of these components prolonged or even increased GPEET expression in the absence of glycerol as well as causing a significant reduction in 5.8S rRNA and its immediate precursor. These results indicate that components of a complex used for rRNA maturation can have an additional role in regulating mRNAs that originate in the nucleolus., (© 2013 John Wiley & Sons Ltd.)

We study finite-time Landau-Zener transitions at a singlet-triplet level crossing in a GaAs double quantum dot, both experimentally and theoretically. Sweeps across the anticrossing in the high driving speed limit result in oscillations with a small visibility. Here we demonstrate how to increase the oscillation visibility while keeping sweep times shorter than T(2)(*) using a tailored pulse with a detuning dependent level velocity. Our results show an improvement of a factor of ~2.9 for the oscillation visibility. In particular, we were able to obtain a visibility of ~0.5 for Stückelberg oscillations, which demonstrates the creation of an equally weighted superposition of the qubit states.

We theoretically investigate the deflection-induced coupling of an electron spin to vibrational motion due to spin-orbit coupling in suspended carbon nanotube quantum dots. Our estimates indicate that, with current capabilities, a quantum dot with an odd number of electrons can serve as a realization of the Jaynes-Cummings model of quantum electrodynamics in the strong-coupling regime. A quantized flexural mode of the suspended tube plays the role of the optical mode and we identify two distinct two-level subspaces, at small and large magnetic field, which can be used as qubits in this setup. The strong intrinsic spin-mechanical coupling allows for detection, as well as manipulation of the spin qubit, and may yield enhanced performance of nanotubes in sensing applications.

We propose a scheme for coherent rotation of the valley isospin of a single electron confined in a carbon nanotube quantum dot. The scheme exploits the ubiquitous atomic disorder of the nanotube crystal lattice, which induces time-dependent valley mixing as the confined electron is pushed back and forth along the nanotube axis by an applied ac electric field. Using experimentally determined values for the disorder strength we estimate that valley Rabi oscillations with a period on the nanosecond time scale are feasible. The valley resonance effect can be detected in the electric current through a double quantum dot in the single-electron transport regime., (© 2011 American Physical Society)

An inducible RNA interference (RNAi) library, consisting of a pool of independent stable transformants with 9-fold genome coverage, was constructed in bloodstream form Trypanosoma brucei using an improved transfection protocol. RNAi induction and selection of resistant parasites was performed in the presence of melarsoprol or eflornithine. The former led to the isolation of the adenosine transporter TbAT1, which is known to be involved in melarsoprol uptake, while the latter identified an amino acid transporter, AAT6. Knockdown of AAT6 reduced mRNA levels to 30-35% in independent clones and increased resistance to eflornithine >5-fold. Genome-wide screens with this library allow an unbiased approach to gene discovery, are extremely rapid and do not exclude essential genes., (Copyright © 2010 Elsevier B.V. All rights reserved.)

We propose and analyze a technique for producing a beam-splitting quantum gate between two modes of a ring-resonator superconducting cavity. The cavity has two integrated superconducting quantum interference devices (SQUIDs) that are modulated by applying an external magnetic field. The gate is accomplished by applying a radio frequency pulse to one of the SQUIDs at the difference of the two mode frequencies. Departures from perfect beam splitting only arise from corrections to the rotating wave approximation; an exact calculation gives a fidelity of >0.9992. Our construction completes the toolkit for linear-optics quantum computing in circuit quantum electrodynamics.

The coat of Trypanosoma brucei consists mainly of glycosylphosphatidylinositol-anchored proteins that are present in several million copies and are characteristic of defined stages of the life cycle. While these major components of the coats of bloodstream forms and procyclic (insect midgut) forms are well characterised, very little is known about less abundant stage-regulated surface proteins and their roles in infection and transmission. By creating epitope-tagged versions of procyclic-specific surface antigen 2 (PSSA-2) we demonstrated that it is a membrane-spanning protein that is expressed by several different life cycle stages in tsetse flies, but not by parasites in the mammalian bloodstream. In common with other membrane-spanning proteins in T. brucei, PSSA-2 requires its cytoplasmic domain in order to exit the endoplasmic reticulum. Correct localisation of PSSA-2 requires phosphorylation of a cytoplasmic threonine residue (T(305)), a modification that depends on the presence of TbMAPK4. Mutation of T(305) to alanine (T(305)A) has no effect on the localisation of the protein in cells that express wild type PSSA-2. In contrast, this protein is largely intracellular when expressed in a null mutant background. A variant with a T(305)D mutation gives strong surface expression in both the wild type and null mutant, but slows growth of the cells, suggesting that it may function as a dominant negative mutant. The PSSA-2 null mutant exhibits no perceptible phenotype in culture and is fully competent at establishing midgut infections in tsetse, but is defective in colonising the salivary glands and the production of infectious metacyclic forms. Given the protein's structure and the effects of mutation of T(305) on proliferation and localisation, we postulate that PSSA-2 might sense and transmit signals that contribute to the parasite's decision to divide, differentiate or migrate.

We theoretically model a nuclear-state preparation scheme that increases the coherence time of a two-spin qubit in a double quantum dot. The two-electron system is tuned repeatedly across a singlet-triplet level anticrossing with alternating slow and rapid sweeps of an external bias voltage. Using a Landau-Zener-Stückelberg model, we find that in addition to a small nuclear polarization that weakly affects the electron spin coherence, the slow sweeps are only partially adiabatic and lead to a weak nuclear spin measurement and a nuclear-state narrowing which prolongs the electron spin coherence. This resolves some open problems brought up by a recent experiment [D. J. Reilly, Science 321, 817 (2008).10.1126/science.1159221]. Based on our description of the weak measurement, we simulate a system with up to n=200 nuclear spins per dot. Scaling in n indicates a stronger effect for larger n.

We study dc charge and spin transport through a weakly coupled quantum dot, driven by a nonadiabatic periodic change of system parameters. We generalize the model of Tien and Gordon to simultaneously oscillating voltages and tunnel couplings. When applying our general result to the two-parameter charge pumping in quantum dots, we find interference effects between the oscillations of the voltage and tunnel couplings. We show that these interference effects may explain recent measurements in metallic islands. Furthermore, we discuss the possibility to electrically pump a spin current in presence of a static magnetic field.

We propose a set of universal gate operations for the singlet-triplet qubit realized by two-electron spins in a double quantum dot, in the presence of a fixed inhomogeneous magnetic field. All gate operations are achieved by switching the potential offset between the two dots with an electrical bias, and do not require time-dependent control of the tunnel coupling between the dots. We analyze the two-electron dynamics and calculate the effective qubit rotation angle as a function of the applied electric bias. We present explicit gate sequences for single-qubit rotations about two orthogonal axes, and a CNOT gate sequence, completing the universal gate set.

WD (tryptophan-aspartic acid dipeptide)-repeat proteins play a central role in signal transduction cascades by co-ordinating the interaction of key signalling molecules. We identified a novel propeller-FYVE [domain identified in Fab1p, YOTB, Vac1p and EEA1 (early endosome antigen 1)] protein, ProF, which is expressed in various cell lines and tissues and consists of seven WD-repeats and a FYVE domain. WD-repeat proteins offer a platform for protein-protein interactions by folding into a seven-bladed propeller-like structure, while the FYVE domain binds to phosphatidylinositol 3-phosphate present mainly on intracellular membranes. The ProF protein partially co-localizes with EEA1 on vesicular structures and binds to the protein kinases Akt and PKCzeta/lambda (protein kinase Czeta/lambda) via its WD-repeat propeller. ProF interacts more strongly with the kinases after hormonal stimulation. Endogenously expressed ProF and the two kinases interact in brain and in the preadipocyte cell line 3T3-L1, suggesting a role in secretory vesicular processes. In summary, we describe a new binding partner for kinases, located on vesicular structures in specialized cells, which may play a role for the spatial organization of signalling cascades.

African trypanosomes undergo differentiation in order to adapt to the mammalian host and the tsetse fly vector. To characterize the role of a mitogen-activated protein (MAP) kinase homologue, TbMAPK5, in the differentiation of Trypanosoma brucei, we constructed a knockout in procyclic (insect) forms from a differentiation-competent (pleomorphic) stock. Two independent knockout clones proliferated normally in culture and were not essential for other life cycle stages in the fly. They were also able to infect immunosuppressed mice, but the peak parasitemia was 16-fold lower than that of the wild type. Differentiation of the proliferating long slender to the nonproliferating short stumpy bloodstream form is triggered by an autocrine factor, stumpy induction factor (SIF). The knockout differentiated prematurely in mice and in culture, suggestive of increased sensitivity to SIF. In contrast, a null mutant of a cell line refractory to SIF was able to proliferate normally. The differentiation phenotype was partially rescued by complementation with wild-type TbMAPK5 but exacerbated by introduction of a nonactivatable mutant form. Our results indicate a regulatory function for TbMAPK5 in the differentiation of bloodstream forms of T. brucei that might be exploitable as a target for chemotherapy against human sleeping sickness.

We study a large ensemble of nuclear spins interacting with a single electron spin in a quantum dot under optical excitation and photon detection. At the two-photon resonance between the two electron-spin states, the detection of light scattering from the intermediate exciton state acts as a weak quantum measurement of the effective magnetic (Overhauser) field due to the nuclear spins. In a coherent population trapping state without light scattering, the nuclear state is projected into an eigenstate of the Overhauser field operator, and electron decoherence due to nuclear spins is suppressed: We show that this limit can be approached by adapting the driving frequencies when a photon is detected. We use a Lindblad equation to describe the driven system under photon emission and detection. Numerically, we find an increase of the electron coherence time from 5 to 500 ns after a preparation time of 10 micros.

A heavy metal responsive gene PvSR3 (GenBank accession number U54703) encoding an acid dehydrin was isolated from a mercuric chloride-treated bean (Phaseolus vulgaris L.) leaf cDNA library by differential screening using cDNAs derived from treated and untreated plants. The PvSR3 cDNA is 981-bp long and has a 606-bp open-reading frame with a 202-residue-deduced amino acid sequence. The PvSR3 sequence contains two conserved repeats of the characteristic lysine-rich K segment (EKKGIMDKIKEKLPG) preceded by an 8-serine residue stretch, whereas the Y segment (DEYGNP) conserved motif is absent. The deduced protein has a calculated molecular weight of 23 kDa and an isoelectric point of 5.2. Sequence similarity and comparative analysis showed that PvSR3 shares 70 and 73% similarity with the dehydrin of poplar and pepper, respectively. Southern hybridizations indicated that PvSR3 was a low copy-number gene. Northern blot analysis revealed that PvSR3 mRNA was weakly detected in seedling leaves. However, the gene expression was strongly stimulated by heavy metals, such as mercury, cadmium, arsenic, and copper, whereas virus infection and salt had little effect on it. In contrast, PvSR3 was not responsive to drought or abscisic acid (ABA), and was downregulated by UV radiation. Furthermore, PvSR3 was upregulated by the exogenous signaling molecules, including salicylic acid (SA) and hydrogen peroxide (H2O2). It is suggested that PvSR3 is extremely related to heavy metal stress, and might play an important role in metal detoxification and resistance to the damage caused by heavy metals.

We determine a lower bound for the entanglement of formation of pairs of electron spins injected into a mesoscopic conductor. The bound can be expressed in terms of experimentally accessible quantities, the zero-frequency current correlators (shot noise power or cross correlators) after transmission through an electronic beam splitter and can be used to gain information about the entanglement from experiment. Spin relaxation (T1 processes) and decoherence (T2) during the ballistic coherent transmission of carriers are taken into account within Bloch theory. A variable inhomogeneous magnetic field gives rise to a useful lower bound for the entanglement of arbitrary states. The decrease in entanglement due to thermally mixed states is studied. Both the entanglement of the output of a source (entangler) and T(1,2) can be determined from current correlators.

We study shot noise for spin-polarized currents and entangled electron pairs in a four-probe (beam-splitter) geometry with a local Rashba spin-orbit (s-o) interaction in the incoming leads. Within the scattering formalism we find that shot noise exhibits Rashba-induced oscillations with continuous bunching and antibunching. We show that entangled states and triplet states can be identified via their Rashba phase in noise measurements. For two-channel leads, we find an additional spin rotation due to s-o induced interband coupling which enhances spin control. We show that the s-o interaction deter-mines the Fano factor, which provides a direct way to measure the Rashba coupling constant via noise.

The role of the two processing sites in the precursor of the small subunit (SS) of ribulose-1,5-bisphosphate carboxylase/oxygenase (pSS) of Chlamydomonas reinhardtii was studied by introducing mutations at the cleavage sites for the stromal processing peptidases SPP-1 and SPP-2, which hydrolyse wild-type pSS (20.6 kDa) to an intermediate-sized product iSS (18.3 kDa) and to the mature SS (16.3 kDa), respectively. The mutations introduced into cDNA resulted in exchange of (a) two amino acids flanking processing site 1, or (b) one or (c) both amino acids flanking processing site 2. Mutation (a) prevented pSS from being processed at site 1 but not from cleavage at site 2. Mutation (c) abolished the action of SPP-2 but not SPP-1. When pSS with mutation (c) was imported into isolated chloroplasts, iSS accumulated while SS formation was abolished. However, mature SS was produced even in the absence of iSS synthesis (mutation a). Import of pSS bearing mutation (b), which only partially inhibited processing at the SPP-2 site, slowed the rate of SS formation down whereas iSS and some slightly smaller derivatives accumulated. These experiments suggested that in Chlamydomonas processing of pSS can occur in two steps, whereby the first step is facultative. The same three mutations were studied in vivo after transformation of SS-deficient C. reinhardtii T60-3 with mutated genomic DNA. Growth and photosynthesis was as in control transformants, except for the slower-growing transformants (mutation c) where no mature SS was immuno-detected. However, pSS fragments with molecular masses between those of iSS and SS were present even in the ribulose-1,5-bisphosphate carboxylase/oxygenase holoenzyme.

We study the effect of the spin-orbit interaction on quantum gate operations based on the spin exchange coupling where the qubit is represented by the electron spin in a quantum dot or a similar nanostructure. Our main result is the exact cancellation of the spin-orbit effects in the sequence producing the quantum XOR gate for the ideal case where the pulse shapes of the exchange and spin-orbit interactions are identical. For the nonideal case, the two pulse shapes can be made almost identical and the gate error is strongly suppressed by two small parameters, the spin-orbit constant and the deviation of the two pulse shapes. We show that the dipole-dipole interaction leads only to very small errors in the XOR gate.

The objective of this open, randomized, multicenter study is to investigate the benefits and economic efficiency of self-management of oral anticoagulation in patients with atrial fibrillation (SMAAF study) in comparison with a group of patients given conventional care by a general practitioner or specialist. Two thousand patients suitable for self-management will be assigned at random to either the self-management group or the control group. The numbers of thromboembolic and hemorrhagic complications requiring treatment during the 2-year follow-up period will be recorded as the primary end point. The secondary endpoint variables will be maintenance of the INR value in the individual target range, INR variance, the course of complications over time, and the cost efficiency of self-management compared with the routine procedures. The last of these parameters will include the diagnostic and/or therapeutic measures carried out, the duration of inpatient hospital treatment, and the social consequences (subsequent rehabilitation treatment, inability to work, forced retirement). The estimate of the required number of patients was based on the assumption that during long-term anticoagulant therapy within the framework of primary and secondary prevention 4% of patients with chronic non-valvular atrial fibrillation would have severe thromboembolic of hemorrhagic complications each year. Since this rate can be halved by self-management, a one-tailed chi 2-test of 80% power and a 5% significance threshold would require n = 997 patients per group. The results of the SMAAF study will establish the socioeconomic benefits of self-management in patients with non-valvular atrial fibrillation.

The present study was carried out to investigate exercise test results and the outcome of the quality of life after administration of trapidil (CAS 15421-84-8, Rocornal) or nifedipine (CAS 21829-25-4) to patients with coronary heart disease. The characteristics of the life quality in combination with the results of exercise test are considered of great importance for selecting medical treatment in patients with chronic stable angina pectoris. However, little information is available on how this first evaluation may be used to select the best pharmacological approach in individual patients. In this prospective multicentre study, 144 patients with stable angina were enrolled in 6 centres. Due to protocol violations and drop-outs 116 patients were evaluated for tolerability; 101 patients were evaluated for efficacy. After baseline evaluation, consisting of an exercise test and a questioning investigating patients' anginal symptoms and several psychometric testings, the patients were randomly allocated to double-blind treatment for 12 weeks with either trapidil, 200 mg t.i.d. or nifedipine, 10 mg t.i.d. according to a parallel group design. After 6 and 12 weeks exercise tests and psychometric testings were repeated. Both trapidil and nifedipine prolonged exercise tolerance (trapidil 39.2% vs. nifedipine 33.3%) or increased the total exercise over baseline levels (trapidil 57.8% vs. nifedipine 61.2%). Using Mann-Whitney U-test the SB-S-rating scale and the physician's assessment revealed a comparable improvement of life quality (trapidil 69.4% vs. nifedipine 80.0%) under both treatments. In addition patient questioning showed a significant reduction in angina attacks and in nitroglycerin consumption. None of the characteristics of anginal symptoms or exercise test gave evidence for a significant difference between nifedipine and trapidil. Both drugs demonstrated similar safety profiles (adverse events (AEs) 12.7% for trapidil and 11.1% for nifedipine); four patients of the trapidil group and one of the nifedipine group discontinued the clinical trial because of AEs. The results of a baseline exercise test and rating questionnaires may offer useful information for selecting medical treatment in stable angina pectoris.

In plants, such as maize, cyclophilin (Cyp) genes are expressed at a basal level in all tissues. Amounts of Cyp mRNA above the basic level are observed in germinating seedlings, in growing tissues/organs such as roots and leaf meristematic tissue of young maize plants, nodes and embryonic female inflorescences of adult plants and also in non-proliferating tissues such as the internodes of adult plants. Salicylic acid (SA) enhances the transcription of maize Cyp genes. The possible involvement of SA in the pathway leading to defense responses induced by abiotic stresses such as mercuric chloride treatment is discussed. A maize Cyp genomic clone isolated using a maize Cyp cDNA probe contains 737 bp of the 5' upstream and the entire coding region. This Cyp gene is not interrupted by intervening sequences. In the 5' upstream region, characteristic transcription signals as well as putative regulatory sequences were identified. Two TATA boxes are found at positions -56 bp and -66 bp with respect to the transcription start site. Two putative heat shock elements were identified in the promoter region; a metal regulatory element and a third heat shock element were localized in the 5' untranslated leader. Several putative polyadenylation signals and (G)T-rich sequence motifs were identified in the 3' untranslated region.

This study investigates the question as to whether, in Helicobacter pylori (H.p.) gastritis, any statistically significant relationships are to be found between the following histological parameters: degree of H.p. colonisation, the degree and activity of gastritis, degree of replacement of the foveolar epithelium by regenerating epithelium, and degree of mucus depletion. Forceps biopsy material obtained from 240 patients with NUD and H.p. gastritis (3 specimens from the antrum, 2 from the corpus) were investigated. The 5 histological parameters employed were graduated semiquantitatively as follows: 0 = normal findings, 1 = minimal, 2 = low-grade, 3 = medium-grade, 4 = high-grade. The evaluation showed that the degree and activity of gastritis, the degree of replacement of foveolar epithelium by regenerating epithelial cells, and the degree of mucus depletion are dependent upon the degree of H.p. colonisation (p < 0.0001). The gastritis parameters were more marked in the antrum than in the corpus. The intercorrelations were highly significant for all five parameters investigated, both in the antrum and corpus (p < 0.0001). On the basis of these results it is concluded that for the histological assessment of H.p. gastritis, in addition to H.p. colonisation, and the degree and activity of gastritis, but also the state of the foveolar epithelium and the mucus production of these epithelial cells should be considered.

Method: The present prospective controlled study investigated the effect of a combination of 500 mg of tannin albuminate and 50 mg ethacridine lactate (Tannacomp) on chronic diarrhea in stable-phase Crohn's disease. Of the 30 patients admitted to the study, Crohn's disease was confined to the small intestine in 5, involved both small and large bowel in 11 patients, and only the large intestine in 14 cases., Treatment: Basic treatment was continued throughout the study; in addition, three times 2 tablets of Tannacomp were administered for 5 days, followed by a 5-day period of no such treatment, and then a further 5 days with the same regimen., Results: At the end of the treatment phases, there was a significant reduction in stool frequency from 5.5 +/- 0.6 (mean +/- SEM) to 4.0 +/- 0.8, and the summed score of the symptoms decreased from 6.3 +/- 0.6 to 5.3 +/- 0.6; in comparison with the initial situation or at the end of the five-day period of no additional treatment, the consistency of the stools also increased. The effect of Tannacomp showed a tendency to be more marked among patients with Crohn's disease limited to the large intestine, as compared with patients with small intestinal involvement. However, before Tannacomp can be recommended as treatment of chronic diarrhea in stable-phase Crohn's disease, further studies are needed.

A long-term study on the therapy of atopic dermatitis with topical urea agents was conducted by over 400 practising dermatologists and pediatricians in Western Germany from March 1989 to March 1991. 1905 patients of all ages who had a baseline diagnosis of acute exacerbation of their neurodermatic skin condition were entered into this open, uncontrolled, multicenter study. Acute attacks were treated with a combination of hydrocortisone and urea. Once the acute symptoms had subsided, therapy was continued with a 10% urea ointment. Over the 12-month observational period, a total of 84% of the patients were exclusively treated with the two trial preparations and only 16% additionally required other corticosteroids.

The amino acid sequences of peptides generated by trypsin and chymotrypsin digestions of the acidic PR4 chitinase from bean were determined. Oligonucleotide primers derived from this sequence were used to synthesize a PR4 chitinase-specific probe by PCR-amplification. This probe allowed the isolation of cDNA clones encoding PR4 chitinase that have been sequenced. This acidic and extracellular chitinase shows some homology to the basic isoform from the same plant, and differs from other known acidic chitinases by the presence of an amino-terminal cysteine-rich domain. Southern blot analysis of bean genomic DNA revealed that PR4 chitinase is encoded by a single gene.

We have established the complete sequence of the 155 amino acid residues of the pathogenesis-related protein PR2 accumulating in bean leaves treated with a mercuric chloride solution. Bean PR2 whose biological function remains to be elucidated, represents a structurally unfamiliar protein in which sequence arginine, cysteine, methionine and tryptophan residues are missing. This sequence is identical to that of bean PvPR1.

Photosystem II-herbicides (bentazone*, diuron) not only block photosynthetic electron transport, but have additional effects on the cell metabolism of Raphanus seedlings. They induce the formation of shade-type chloroplasts with a different ultrastructure and prenyllipid composition. This is shown by higher grana stacks as well as by higher chlorophyll b and lutein amounts with reference to chlorophyll a, and lower levels of the plastidic prenylquinones (plastoquinone, phylloquinone, α-tocoquinone) and β-carotene as compared to the controls.The two herbicides bentazone and diuron change the labelling pattern of the chloroplast pigments from (3)H-mevalonic acid and 2-(14)C-acetate and also reduce the accumulation of anthocyanin (pelargonidin), which is a further indication of a shade-type growth response. The level of ubiquinone, an indicator for mitochondrial activity, is, however, increased.

A double-blind study was carried out on 56 geronto-psychiatric in-patients who suffered from cerebral metabolic and nutritional disturbances to prove the effectiveness of 10-methoxy-1,6-dimethyl-ergoline-8 beta-methanol-(5-bromonicotinate (nicergoline, Sermion). After a washout-phase of eight days the patients in the verum group received 3 x 1 dragée at 10 mg for a period of 12 weeks. For methodical reasons only patients with slight transit syndromes and, of these, only the first four weeks of examination were included in the present analysis. Thus 8 verum and 9 placebo patients remain whose findings during the trial are recorded in three procedures of capacity and two procedures of self-assessment (syndrome short test, repeating figures and letters, reading letters; scale for general somatic discomfort, scale for vegetative functional disturbances). In the measuring procedures there is a tendency towards improvement under the treatment with nicergline compared with placebo during the first three weeks. But the present results are not sufficient to come to a clear decision on the effectiveness of nicergoline in patients with cerebrovascular insufficiency.

A statistical model for long-term follow-up of glaucomatous visual fields is described. Using an analysis of individual testpoints, a statistical evaluation of visual field change is done by the Bowker symmetry test. Eccentricity of test points in the visual field, density of scotomas and number of defective test points were used as parameters. The authors demonstrate that evaluation with this method is superior to methods using total sensitivity loss or mean sensitivity of the visual field. This model is currently being used in a retrospective and a prospective glaucoma study.

A minimum of 37 genes corresponding to tRNAs for 17 different amino acids have been localized on the restriction endonuclease cleavage site map of theZea mays chloroplast DNA molecule. Of these, 14 genes corresponding to tRNAs for 11 amino acids are located in the larger of the two single-copy regions which separate the two inverted copies of the repeat region. One tRNA gene is in the smaller single-copy region. Each copy of the large repeated sequence contains, in addition to the ribosomal RNA genes, 11 tRNA genes corresponding to tRNAs for 8 amino acids. The genes for tRNA2 (Ile) and tRNA(Ala) map in the ribosomal spacer sequence separating the 16S and 23S ribosomal RNA genes. The three isoaccepting species for the tRNAs(Leu) and the three for tRNAs(Ser), as well as the two isoaccepting species for tRNA(Asn), tRNA(Gly), tRNAs(Ile), tRNAs(Met), tRNAs(Thr), are shown to be encoded at different loci.Two independent methods have been used for the localization of tRNA genes on the physical map of the maize chloroplast DNA molecule: (a) cloned chloroplast DNA fragments were hybridized with radioactively-labelled total 4S RNAs, the hybridized RNAs were then eluted, and identified by two-dimensional polyacrylamide gel electrophoresis, and (b) individual tRNAs were(32)P-labelledin vitro and hybridized to DNA fragments generated by digestion of maize chloroplast DNA with various restriction endonucleases.