Evaluation of the performance of multiple immunoassay diagnostic platforms on the National Microbiology Laboratory SARS-CoV-2 National Serology Panel

BACKGROUND

Serological assays designed to detect SARS-CoV-2 antibodies are being used in serological surveys and other specialized applications. As a result, and to ensure that the outcomes of serological testing meet high quality standards, evaluations are required to assess the performance of these assays and the proficiency of laboratories performing them.

METHODS

A panel of 60 plasma/serum samples from blood donors who had reverse transcriptase-polymerase chain reaction (RT-PCR) confirmed SARS-CoV-2 infections and 21 SARS-CoV-2 negative samples were secured and distributed to interested laboratories within Canada (n = 30) and the United States (n = 1). Participating laboratories were asked to provide details on the diagnostic assays used, the platforms the assays were performed on, and the results obtained for each panel sample. Laboratories were blinded with respect to the expected outcomes.

RESULTS

The performance of the different assays evaluated was excellent, with the high-throughput platforms of Roche, Ortho, and Siemens demonstrating 100% sensitivity. Most other high-throughput platforms had sensitivities of >93%, with the exception of the IgG assay using the Abbott ARCHITECT which had an average sensitivity of only 87%. The majority of the high-throughput platforms also demonstrated very good specificities (>97%).

CONCLUSION

This proficiency study demonstrates that most of the SARS-CoV-2 serological assays utilized by provincial public health or hospital laboratories in Canada have acceptable sensitivity and excellent specificity.

Paramagnetic probes in an organic semiconductor: μSR and DFT calculations of the Mu adducts of Alq3 and 8-hydroxyquinoline

It has been claimed that longitudinal field muon spin relaxation (LF-μSR) experiments on the organic semiconductor (OSC) tris-(8-hydroxyquinoline)aluminum(III) (Alq₃) have measured electron hopping rates of ∼10¹²s^-1, while density functional theory (DFT) calculations suggest that electron hopping between a muoniated radical and a neighboring molecule is energetically unfavorable and that the LF-μSR experiments were probing muoniated radicals with localized spin density. We have performed avoided level crossing muon spin resonance (ALC-μSR) and transverse field muon spin rotation (TF-μSR) measurements on Alq₃ and 8-hydroxyquinoline (8hq), which is meant to model the muoniated radicals present in Alq₃ when they are not in an OSC. These are supplemented by benchmarked DFT calculations. The ALC-μSR and TF-μSR spectra of 8hq and Alq₃ are best explained by Mu adding to all six secondary carbons of the quinolate rings with roughly equal yields and localized spin density. There is no evidence in the TF-μSR spectrum of Alq₃ for the formation of radicals with muon hyperfine coupling constants of 23 or 91 MHz as reported earlier by others. Our measurements support the view that there is localized spin density on the molecule to which Mu is covalently bound and the muon is not a passive probe in organic systems as it can be incorporated into radicals that have different electronic structures to the parent compounds. The muoniated radicals in Alq₃ are more short-lived than in 8hq, which could be due to interactions with mobile electrons in the OSC, but with electron spin flip rates on the order of ∼10⁷s^-1.

Dynamics and local environment of an aromatic counterion bound to di-chain cationic surfactant bilayers studied by avoided level crossing muon spin resonance: evidence for counterion condensation

Avoided level crossing muon spin resonance (ALC-μSR) has been used to study the reorientational dynamics of muon-spin-labelled 2,4,6-trimethylbenzoate (246TMB^-) counterions and their interaction with DODMAC (dioctadecyldimethylammonium chloride) bilayers in the L_α and L_β liquid crystalline states. The muoniated radical anion formed by the addition of muonium to the secondary carbons of the aromatic ring of 246TMB^- is used as a local spin probe. The muon and methylene proton hyperfine parameters and the electron spin relaxation rate (λ_e) of the muoniated spin probe were determined as a function of temperature by modelling the ALC-μSR spectra with Monte Carlo numerical simulations. The observation of a Δ₁ resonance indicates that 246TMB^- is undergoing anisotropic motion and doesn't reside in the aqueous layer in either the L_α and L_β phases. The lack of an abrupt change in the hyperfine parameters or λ_e when the system goes from the L_β to the L_α lamellar liquid crystalline phases suggests that 246TMB^- is located at the oil-water interface rather than within the bilayer. The hyperfine parameters indicate that 246TMB^- is undergoing large amplitude reorientational motion about a preferred orientation resulting from the bilayer's electric field. The interaction between 246TMB^- and the bilayer decreases and the amplitude of the wobbling-in-a-cone motion increases with increasing temperature. The temperature dependence of the electron spin relaxation rate indicates the barrier to reorientation is 41.7 kJ mol^-1.

The new versatile general purpose surface-muon instrument (GPS) based on silicon photomultipliers for μSR measurements on a continuous-wave beam

We report on the design and commissioning of a new spectrometer for muon-spin relaxation/rotation studies installed at the Swiss Muon Source (SμS) of the Paul Scherrer Institute (PSI, Switzerland). This new instrument is essentially a new design and replaces the old general-purpose surface-muon (GPS) instrument that has been for long the workhorse of the μSR user facility at PSI. By making use of muon and positron detectors made of plastic scintillators read out by silicon photomultipliers, a time resolution of the complete instrument of about 160 ps (standard deviation) could be achieved. In addition, the absence of light guides, which are needed in traditionally built μSR instrument to deliver the scintillation light to photomultiplier tubes located outside magnetic fields applied, allowed us to design a compact instrument with a detector set covering an increased solid angle compared with the old GPS.

Partitioning of 2-phenylethanol and limonene cosurfactants in C12E4

Avoided level-crossing muon spin resonance (ALC-μSR) has been used to study the dynamics and local environment of spin probes formed by muonium (Mu) addition to 2-phenylethanol (PEA) and limonene (1-methyl-4-(1-methylethenyl)-cyclohexene) in an aqueous dispersion of the nonionic surfactant C₁₂E₄ (tetra(ethylene glycol) n-dodecyl ether). The spin probes derived from both cosurfactants reside within the micelles in the L₁ phase and the bilayers in the L_α phase rather than in the aqueous region. The local polarity measured by the different isomers of the Mu adducts of PEA suggests there is a water gradient within the micelles and bilayers. Slow rotation of the micelles broadened the Δ₁ resonances with increasing temperature in the L₁ phase while narrower Δ₁ resonances were observed in the L_α phase due to the rapid rotation of the spin probes around a preferred axis, which was wobbling within a cone.

A mathematical framework for virtual IMRT QA using machine learning

PURPOSE

It is common practice to perform patient-specific pretreatment verifications to the clinical delivery of IMRT. This process can be time-consuming and not altogether instructive due to the myriad sources that may produce a failing result. The purpose of this study was to develop an algorithm capable of predicting IMRT QA passing rates a priori.

METHODS

From all treatment, 498 IMRT plans sites were planned in eclipse version 11 and delivered using a dynamic sliding window technique on Clinac iX or TrueBeam Linacs. 3%/3 mm local dose/distance-to-agreement (DTA) was recorded using a commercial 2D diode array. Each plan was characterized by 78 metrics that describe different aspects of their complexity that could lead to disagreements between the calculated and measured dose. A Poisson regression with Lasso regularization was trained to learn the relation between the plan characteristics and each passing rate.

RESULTS

Passing rates 3%/3 mm local dose/DTA can be predicted with an error smaller than 3% for all plans analyzed. The most important metrics to describe the passing rates were determined to be the MU factor (MU per Gy), small aperture score, irregularity factor, and fraction of the plan delivered at the corners of a 40 × 40 cm field. The higher the value of these metrics, the worse the passing rates.

CONCLUSIONS

The Virtual QA process predicts IMRT passing rates with a high likelihood, allows the detection of failures due to setup errors, and it is sensitive enough to detect small differences between matched Linacs.

Rate of Molecular Transfer of Allyl Alcohol across an AOT Surfactant Layer Using Muon Spin Spectroscopy

The transfer rate of a probe molecule across the interfacial layer of a water-in-oil (w/o) microemulsion was investigated using a combination of transverse field muon spin rotation (TF-μSR), avoided level crossing muon spin resonance (ALC-μSR), and Monte Carlo simulations. Reverse microemulsions consist of nanometer-sized water droplets dispersed in an apolar solvent separated by a surfactant monolayer. Although the thermodynamic, static model of these systems has been well described, our understanding of their dynamics is currently incomplete. For example, what is the rate of solute transfer between the aqueous and apolar solvents, and how this is influenced by the structure of the interface? With an appropriate choice of system and probe molecule, μSR offers a unique opportunity to directly probe these interfacial transfer dynamics. Here, we have employed a well characterized w/o microemulsion stabilized by bis(2-ethylhexyl) sodium sulfosuccinate (Aerosol OT), with allyl alcohol (CH2═CH-CH2-OH, AA) as the probe. Resonances due to both muoniated radicals, CMuH2-C*H-CH2-OH and C*H2-CHMu-CH2-OH, were observed with the former being the dominant species. All resonances displayed solvent dependence, with those in the microemulsion observed as a single resonance located at intermediate magnetic fields to those present in either of the pure solvents. Observation of a single resonance is strong evidence for interfacial transfer being in the fast exchange limit. Monte Carlo calculations of the ΔM = 0 ALC resonances are consistent with the experimental data, indicating exchange rates greater than 10(9) s(-1), placing the rate of interfacial transfer at the diffusion limit.

Direct spectroscopic observation of a shallow hydrogenlike donor state in insulating SrTiO3

We present a direct spectroscopic observation of a shallow hydrogenlike muonium state in SrTiO(3) which confirms the theoretical prediction that interstitial hydrogen may act as a shallow donor in this material. The formation of this muonium state is temperature dependent and appears below ∼ 70K. From the temperature dependence we estimate an activation energy of ∼ 50 meV in the bulk and ∼ 23 meV near the free surface. The field and directional dependence of the muonium precession frequencies further supports the shallow impurity state with a rare example of a fully anisotropic hyperfine tensor. From these measurements we determine the strength of the hyperfine interaction and propose that the muon occupies an interstitial site near the face of the oxygen octahedron in SrTiO(3). The observed shallow donor state provides new insight for tailoring the electronic and optical properties of SrTiO(3)-based oxide interface systems.

Hyperfine coupling constants of the cyclohexadienyl radical in benzene and dilute aqueous solution

The muon hyperfine coupling constant (Aμ) of the muoniated cyclohexadienyl radical (C6H6Mu) has been directly measured in a 5 mM solution of benzene in water by the radio-frequency muon spin resonance (RF-μSR) technique. The relative shift of Aμ in aqueous solution compared with the value in neat benzene (ΔAμ/Aμ = +0.98(5)% at 293 K) can now be compared directly with theoretical predictions. Application of the RF-μSR method to other dilute systems will provide extremely important information on understanding solvent effects.

New Vesicle Gels in Household Applications

Stable dispersions of either gas bubbles or solid particles like abrasives become increasingly attractive for the home care market. The property to yield a stable dispersion is not necessarily linked to a high viscosity in general but requires a highly viscous, solid-like behaviour under rest as well as a liquid-like flow behaviour under shear. A gel comprising such a yield zone can be obtained by creating multi-lamellar vesicles with a rather stiff shell. Due to the repulsion forces of opposite electric charges the combination of suitable anionic and cationic surfactants yields vesicles that are inflexible enough to comprise a yield zone. Surfactants which are appropriate to yield suitable vesicle gels can be chosen according to their spatial dimensions since the geometry of the molecules determines their aggregation behaviour. With this, new formulation possibilities for bathroom cleaners or scouring liquids are available.

Muoniated spin probes in the discotic liquid crystal HHTT: rapid electron spin relaxation in the hexagonal columnar and isotropic phases

Avoided level crossing muon spin resonance (ALC-μSR) spectroscopy was used to study radicals produced by the addition of the light hydrogen isotope muonium (Mu) to the discotic liquid crystal (DLC) 2,3,6,7,10,11-hexahexylthiotriphenylene (HHTT). Mu adds to the secondary carbon atoms of HHTT to produce a substituted cyclohexadienyl radical, whose identity was confirmed by comparing the measured hyperfine coupling constants with values obtained from DFT calculations. ALC-μSR spectra were obtained in the isotropic (I), hexagonal columnar (Col(h)), helical (H), and crystalline (Cr) phases. In the I and Col(h) phases the radicals, which are incorporated within the stacks of HHTT molecules as isolated paramagnetic defects, undergo extremely rapid electron spin relaxation, on the order of a hundredfold faster than in the H or Cr phases. The electron spin relaxation rate increases significantly with increasing temperature and appears to be caused by the liquidlike motion within the columns, which modulates the overlap between the π system of the radical and the π systems of the neighboring HHTT molecules, and hence, the hyperfine coupling constants. Rapid electron spin relaxation should occur for any π radical incorporated within the columns of a DLC, which may limit the utility of DLCs for future spin-based technologies.

Photo-induced persistent inversion of germanium in a 200-nm-deep surface region

The controlled manipulation of the charge carrier concentration in nanometer thin layers is the basis of current semiconductor technology and of fundamental importance for device applications. Here we show that it is possible to induce a persistent inversion from n- to p-type in a 200-nm-thick surface layer of a germanium wafer by illumination with white and blue light. We induce the inversion with a half-life of ~12 hours at a temperature of 220 K which disappears above 280 K. The photo-induced inversion is absent for a sample with a 20-nm-thick gold capping layer providing a Schottky barrier at the interface. This indicates that charge accumulation at the surface is essential to explain the observed inversion. The contactless change of carrier concentration is potentially interesting for device applications in opto-electronics where the gate electrode and gate oxide could be replaced by the semiconductor surface.

How do strain and steric interactions affect the reactions of aromatic compounds with free radicals? Characterization of the radicals formed by muonium addition to p-xylene and [2.2]paracyclophane by DFT calculations and muon spin spectroscopy

Muoniated radicals were produced by the addition of muonium (Mu) to the aromatic compound p-xylene (1) in the solid and liquid states and to the strained aromatic compound [2.2]paracyclophane (2) in the solid state. The radicals were characterized by avoided level crossing muon spin resonance spectroscopy and identified by comparing the experimentally determined muon hyperfine coupling constants with values obtained from DFT calculations. Mu was observed to add to both the secondary and tertiary carbons of 1, with the relative yield of the Mu adduct of the tertiary carbons estimated to be ∼10% in the liquid phase. The relative yield of the tertiary adduct is much higher in the solid state although this cannot be calculated exactly due to the overlap of resonances and the apparent nonuniform distribution of the radical orientations. There are three possible addition sites in 2 due to the lower symmetry of the six-membered ring compared with 1. Mu can add to the secondary carbons either from the outside of 2, generating the "exo" adduct, or from the inside, generating the "endo" adduct. The relative yields of the exo, endo, and tertiary carbon adducts are 67.1(1), 21.8(1), and 11.1(1)%, respectively. The barriers to Mu addition at the different sites of isolated molecules were determined from DFT calculations. The barriers for Mu addition to 2 are lower than the barriers for Mu addition to 1, except for addition to the "endo" position, where the unfavorable steric interactions with the second ring of 2 raise the addition barrier considerably. The measured relative yields do not reflect the distribution of products calculated using the activation energies obtained from the DFT calculations due to strong steric interactions with neighboring molecules.

Molecular dynamics in rod-like liquid crystals probed by muon spin resonance spectroscopy

Muoniated spin probes were produced by the addition of muonium (Mu) to two rod-like liquid crystals: N-(4-methoxybenzylidene)-4'-n-butylaniline (MBBA) and cholesteryl nonanoate (CN). Avoided level crossing muon spin resonance spectroscopy was used to characterize the muoniated spin probes and to probe dynamics at the molecular level. In MBBA Mu adds predominantly to the carbon of the bridging imine group and the muon and methylene proton hyperfine coupling constants (hfccs) of the resulting radical shift in the nematic phase due to the dipolar hyperfine coupling, the ordering of the molecules along the applied magnetic field and fluctuations about the local director. The amplitude of these fluctuations in in the nematic phase of MBBA is determined from the temperature dependence of the methylene proton hfcc. Mu adds to the double bond of the steroidal ring system of CN and the temperature dependence of the Δ(1) line width provides information about the amplitude of the fluctuations about the local director in the chiral nematic phase and the slow isotropic reorientation in the isotropic phase.

Design and commissioning of a high magnetic field muon spin relaxation spectrometer at the ISIS pulsed neutron and muon source

The high magnetic field (HiFi) muon instrument at the ISIS pulsed neutron and muon source is a state-of-the-art spectrometer designed to provide applied magnetic fields up to 5 T for muon studies of condensed matter and molecular systems. The spectrometer is optimised for time-differential muon spin relaxation studies at a pulsed muon source. We describe the challenges involved in its design and construction, detailing, in particular, the magnet and detector performance. Commissioning experiments have been conducted and the results are presented to demonstrate the scientific capabilities of the new instrument.

Muon spin spectroscopy of the discotic liquid crystal HAT6

Avoided level crossing muon spin resonance (ALC-muSR) has been used to study the cyclohexadienyl-type radicals produced by the addition of muonium (Mu) to the discotic liquid crystal HAT6 (2,3,6,7,10,11-hexahexyloxytriphenylene) in the crystalline (Cr) phase, the hexagonal columnar mesophase (Col(h)) and isotropic (I) phase. In the Cr phase unpaired electron spin density can be transferred from the radical to neighboring HAT6 molecules depending on the overlap of their pi-systems and hence on the relative orientation of the triphenylene rings. The two Delta(1) resonances in the ALC-muSR spectra of the Cr phase indicate that the neighboring HAT6 molecules have two preferred orientations with respect to the radical: one which results in negligible spin density transfer and a second where 17% of the unpaired spin density is transferred. The ALC-muSR spectra in Col(h) and I phases are substantially different from those of the Cr phase in that there are two narrow resonances superimposed on an extremely broad and intense resonance. The narrow resonances are due to highly mobile radicals located in the aliphatic region between the columns and the broad resonance is due to radicals incorporated within the columns of HAT6 molecules. The large width and amplitude of this resonance indicates that the radicals within the columns are undergoing rapid electron spin relaxation but the mechanism that causes this relaxation is unknown.

Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation

Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve and find the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance.

Intrinsic mobility limit for anisotropic electron transport in Alq3

Muon spin relaxation has been used to probe the charge carrier motion in the molecular conductor Alq3 (tris[8-hydroxy-quinoline] aluminum). At 290 K, the magnetic field dependence of the muon spin relaxation corresponds to that expected for highly anisotropic intermolecular electron hopping. Intermolecular mobility in the fast hopping direction has been found to be 0.23+/-0.03 cm2 V-1 s(-1) in the absence of an electric- field gradient, increasing to 0.32+/-0.06 cm2 V-1 s(-1) in an electric field gradient of 1 MV m(-1). These intrinsic mobility values provide an estimate of the upper limit for mobility achievable in bulk material.

Local Ordering in Liquids: Solvent Effects on the Hyperfine Couplings of the Cyclohexadienyl Radical

Ordering of solvent molecules in the vicinity of a dipolar free radical affects its hyperfine coupling constants (hfcs). Specifically, it is demonstrated how the variation of the experimental methylene proton and muon hfcs of the muoniated cyclohexadienyl radical in several solvents and solvent mixtures of varying polarity can be accounted for by a dipole-dipole reaction field model that is based on the model of Reddoch and Konishi (J. Chem. Phys. 1979, 70, 2121) which was developed to explain the solvent dependence of the 14N hfc in the di-tert-butyl-nitroxide radical. Ab initio calculations were carried out with the cyclohexadienyl radical in an electric field to model the electric field arising from the electric dipole moments of the surrounding solvent molecules. An extension of the model that includes the dipole-quadrupole interaction can account for the larger hfc in benzene compared with that in octadecane, and it is predicted that the hfc will be proportional to the concentration of quadrupole moments to the 4/3 power. The influence of hydrogen bonding between the radicals' pi electrons and the OH groups of the solvent on the hfcs is also discussed. Comparison with gas-phase data permits a separation of vibrational effects and reveals that approximately 28% of the temperature dependence in water is due to increasing solvent disorder.

Using spin polarised positive muons for studying guest molecule partitioning in soft matter structures

Fully polarised positive muons substituted for protons in organic free radicals can be used as spin labels which reveal information about the structure, dynamics and environment of these radicals. In applications via the technique of avoided-level-crossing muon spin resonance (ALC-microSR), the positive muon has been used to study the partitioning of phenyl alcohols in lamellar phase colloidal dispersions of a cationic dichain surfactant. Here we describe the experimental technique which permits highly sensitive spectroscopy as previously demonstrated for surfactant mixtures. We also demonstrate its capability in the study of partitioning of cosurfactant molecules in surfactant bilayers in order to elucidate the main factors which contribute to cosurfactant ordering at interfaces. The technique takes advantage of the positive muon combining with an electron to a hydrogen-like atom that is called muonium. This atom attaches to a phenyl group, forming a cyclohexadienyl-type radical that contains the muon as a polarised spin label, providing an excellent probe even for very low phenyl alcohol concentrations. The position of one type of resonance, which on the basis of spectroscopic selection rules is denoted as Delta(0), is related to the solvent polarity of the radicals' environment. The results derived from Delta(0) measurements reveal a systematic trend where the increasing chain length of the phenyl alcohol results in a deeper immersion of the phenyl ring of the alcohol into the surfactant bilayer with the OH group anchored at the interface. In addition, the data suggest partial penetration of water molecules into the bilayer. Furthermore, data ensuing from a second resonance (called Delta(1), which is dependent upon the degree of confinement of the radical within the surfactant aggregate structure) indicates not only that the phenyl alcohol resides in an anisotropic environment, (i.e. that the host molecule is unable to undergo full 3-D reorientation on a timescale of 50 ns), but the resonance line widths indicate that the radicals are undergoing fast rotation about a particular axis, in this instance about the first C-C substituent bond at the phenyl ring. Detailed analysis of these Delta(1) line shapes suggests that other types of motion involving reorientation of the above rotation axis are also present. At room temperature, the hydrocarbon chains of the double layers form an aggregate state commonly referred to as the L(beta) phase, where the motions of surfactant alkyl chains are effectively frozen out. These chains melt on heating over a temperature range which is solution composition dependent (ca. 51 to 67 degrees C), but in all cases leading to a liquid-like disordered hydrocarbon regime whilst retaining the overall lamellar structure (and in this state is termed L(alpha)). Above the L(alpha)/L(beta) chain ordering phase transition the tracer molecules reside within the bilayer, but below this transition (and depending on their water-oil solubility) they are completely or partly expelled. This interpretation is further supported by Heisenberg spin exchange experiments. The water-bilayer partitioning reflects both typical classical and nonclassical hydrophobic solvation depending on temperature and chain length of phenyl alcohols.

Partitioning of small amphiphiles at surfactant bilayer/water interfaces: an avoided level crossing muon spin resonance study

The temperature-dependent variation of local environment and reorientation dynamics of the small amphiphile 2-phenylethanol in lamellar phase dispersions of the dichain cationic surfactants, 2,3-diheptadecyl ester ethoxypropyl-1,1,1-trimethylammonium chloride (DHTAC) and dioctadecyldimethylammonium chloride (DODMAC), and the nonionic surfactant, tetra(ethylene glycol) n-dodecyl ether (C12E4), have been determined using avoided level crossing muon spin resonance spectroscopy (ALC-muSR). For cosurfactant radicals the hydrophobic or hydrophilic character of the surrounding media can be determined from their magnetic resonance signatures. Comparison of the three different bilayer-forming surfactant systems shows that the ALC-muSR technique is able to distinguish both major and subtle differences in the partitioning of the cosurfactant radicals between the different systems.

The immunoglobulin heavy-chain matrix-associating regions are bound by Bright: a B cell-specific trans-activator that describes a new DNA-binding protein family

B lymphocyte-restricted transcription of immunoglobulin heavy-chain (IgH) genes is specified by elements within the variable region (VH) promoter and the intronic enhancer (E mu). The gene encoding a protein that binds a VH promoter proximal site necessary for induced mu-heavy-chain transcription has been cloned. This B-cell specific protein, termed Bright (B cell regulator of IgH transcription), is found in both soluble and matrix insoluble nuclear fractions. Bright binds the minor groove of a restricted ATC sequence that is sufficient for nuclear matrix association. This sequence motif is present in previously described matrix-associating regions (MARs) proximal to the promoter and flanking E mu. Bright can activate E mu-driven transcription by binding these sites, but only when they occur in their natural context and in cell lines permissive for E mu activity. To bind DNA, Bright requires a novel tetramerization domain and a previously undescribed domain that shares identity with several proteins, including SWI1, a component of the SWI/SNF complex.

[Early functional treatment of the injured shoulder supported by an active shoulder bandage]

The following study shows the results of treatment of 29 patients suffering from rotatory cuff lesion and of 20 patients with tendinosis. The results of functional physiotherapy of the patients with rotatory cuff lesion correspond to the results of post-operative treatment described in other studies. As a result of early functional physiotherapy backed up by an active shoulder support, the treatment was both improved and shortened considerably. The accompanying pain relief achieved an earlier usability of the shoulder joint in both groups of patients. Four patients with rotatory cuff lesions were resistant to physiotherapy and finally had to undergo surgery.

Simultaneous gas exchange and fluorescence measurements indicate differences in the response of sunflower, bean and maize to water stress

Gas exchange and fluorescence measurements of attached leaves of water stressed bean, sunflower and maize plants were carried out at two light intensities (250 μmol quanta m(-2)s(-1) and 850 μmol quanta m(-2)s(-1)). Besides the restriction of transpiration and CO2 uptake, the dissipation of excess light energy was clearly reflected in the light and dark reactions of photosynthesis under stress conditions. Bean and maize plants preferentially use non-photochemical quenching for light energy dissipation. In sunflower plants, excess light energy gave rise to photochemical quenching. Autoradiography of leaves after photosynthesis in (14)CO2 demonstrated the occurrence of leaf patchiness in sunflower and maize but not in bean. The contribution of CO2 recycling within the leaves to energy dissipation was investigated by studies in 2.5% oxygen to suppress photorespiration. The participation of different energy dissipating mechanisms to quanta comsumption on agriculturally relevant species is discussed.

Light Energy Dissipation under Water Stress Conditions: Contribution of Reassimilation and Evidence for Additional Processes

Using (14)CO(2) gas exchange and metabolite analyses, stomatal as well as total internal CO(2) uptake and evolution were estimated. Pulse modulated fluorescence was measured during induction and steady state of photosynthesis. Leaf water potential of Digitalis lanata EHRH. plants decreased to -2.5 megapascals after withholding irrigation. By osmotic adjustment, leaves remained turgid and fully exposed to irradiance even at severe water stress. Due to the stress-induced reduction of stomatal conductance, the stomatal CO(2) exchange was drastically reduced, whereas the total CO(2) uptake and evolution were less affected. Stomatal closure induced an increase in the reassimilation of internally evolved CO(2). This ;CO(2) recycling' consumes a significant amount of light energy in the form of ATP and reducing equivalents. As a consequence, the metabolic demand for light energy is only reduced by about 40%, whereas net photosynthesis is diminished by about 70% under severe stress conditions. By CO(2) recycling, carbon flux, enzymatic substrate turnover and consumption of light energy were maintained at high levels, which enabled the plant to recover rapidly after rewatering. In stressed D. lanata plants a variable fluorescence quenching mechanism, termed ;coefficient of actinic light quenching,' was observed. Besides water conservation, light energy dissipation is essential and involves regulated metabolic variations.

Identification of the epsilon-subunit of Escherichia coli DNA polymerase III holoenzyme as the dnaQ gene product: a fidelity subunit for DNA replication

Based on extensive genetic and biochemical studies, the multisubunit DNA polymerase III holoenzyme is considered responsible for the chain-elongation stage in replication of the genome of Escherichia coli and is thus expected to be the major determinant of fidelity as well. Previous experiments have shown that two mutations conferring a very high mutation rate on E. coli, mutD5 and dnaQ49, decrease severely the 3' leads to 5' exonucleolytic editing activity of the polymerase III holoenzyme. To identify more precisely the nature of these mutations, we have carried out genetic mapping and complementation experiments. From these studies and experiments by others, we conclude that the most potent general mutator mutations in E. coli occur in a single gene, dnaQ. To define further the role of the dnaQ gene, we have used two-dimensional gel electrophoresis to compare the labeled dnaQ gene product with purified polymerase III holoenzyme. The dnaQ product comigrates with the epsilon-subunit, a 25-kilodalton protein of the polymerase III "core" enzyme. We conclude that the epsilon-subunit of polymerase III holoenzyme has a special role in defining the accuracy of DNA replication, probably through control of the 3' leads to 5' exonuclease activity.