Showing papers by "Free University of Berlin published in 1992"

The spectral input systems of hymenopteran insects and their receptor-based colour vision.

Abstract: Spectral sensitivity functions S(λ) of single photoreceptor cells in 43 different hymenopteran species were measured intracellularly with the fast spectral scan method. The distribution of maximal sensitivity values (λmax) shows 3 major peaks at 340 nm, 430 nm and 535 nm and a small peak at 600 nm. Predictions about the colour vision systems of the different hymenopteran species are derived from the spectral sensitivities by application of a receptor model of colour vision and a model of two colour opponent channels. Most of the species have a trichromatic colour vision system. Although the S(λ) functions are quite similar, the predicted colour discriminability curves differ in their relative height of best discriminability in the UV-blue or bluegreen area of the spectrum, indicating that relatively small differences in the S(λ) functions may have considerable effects on colour discriminability. Four of the hymenopteran insects tested contain an additional R-receptor with maximal sensitivity around 600 nm. The R-receptor of the solitary bee Callonychium petuniae is based on a pigment (P596) with a long λmax, whereas in the sawfly Tenthredo campestris the G-receptor appears to act as filter to a pigment (P570), shifting its λmax value to a longer wavelength and narrowing its bandwidth. Evolutionary and life history constraints (e.g. phylogenetic relatedness, social or solitary life, general or specialized feeding behaviour) appear to have no effect on the S(λ) functions. The only effect is found in UV receptors, for which λmax values at longer wavelengths are found in bees flying predominantly within the forest.

Blood viscosity in tube flow: dependence on diameter and hematocrit

Abstract: Since the original publications by Martini et al. (Dtsch. Arch. Klin. Med. 169: 212–222, 1930) and Fahraeus and Lindqvist (Am. J. Physiol. 96: 562–568, 1931), it has been known that the relative ap...

Ca2+/calmodulin-dependent formation of hydrogen peroxide by brain nitric oxide synthase.

Abstract: L-Arginine-derived nitric oxide (NO) acts as an inter- and intra-cellular signal molecule in many mammalian tissues including brain, where it is formed by a flavin-containing Ca2+/calmodulin-requiring NO synthase with NADPH, tetrahydrobiopterin (H4biopterin) and molecular oxygen as cofactors. We found that purified brain NO synthase acted as a Ca2+/calmodulin-dependent NADPH:oxygen oxidoreductase, catalysing the formation of hydrogen peroxide at suboptimal concentrations of L-arginine or H4biopterin, which inhibited the hydrogen peroxide formation with half-maximal effects at 11 microM and 0.3 microM respectively. Half-maximal rates of L-citrulline formation were observed at closely similar concentrations of these compounds, indicating that the NO synthase-catalysed oxygen activation was coupled to the synthesis of L-citrulline and NO in the presence of L-arginine and H4biopterin. N omega-Nitro-L-arginine, its methyl ester and N omega-monomethyl-L-arginine inhibited the synthesis of L-citrulline from L-arginine (100 microM) with half-maximal effects at 0.74 microM, 2.8 microM and 15 microM respectively. The N omega-nitro compounds also blocked the substrate-independent generation of hydrogen peroxide, whereas N omega-monomethyl-L-arginine did not affect this reaction. According to these results, activation of brain NO synthase by Ca2+ at subphysiological levels of intracellular L-arginine or H4biopterin may result in the formation of reactive oxygen species instead of NO, and N omega-nitro-substituted L-arginine analogues represent useful tools to effectively block NO synthase-catalysed oxygen activation.

Controlled-valence properties of La1-xSrxFeO3 and La1-xSrxMnO3 studied by soft-x-ray absorption spectroscopy.

Abstract: The controlled-valence properties of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ and ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ are studied by means of soft-x-ray absorption spectroscopy. A comparison between the transition-metal 2p spectra and atomic-multiplet calculations is used to determine the 3d count. The O 1s spectrum is used to characterize changes in unoccupied states that contain oxygen p character. The results indicate that the holes induced by substitution for both series are located in states of mixed metal 3d--oxygen 2p character. The ground state of ${\mathrm{LaFeO}}_{3}$ is mainly 3${\mathit{d}}^{5}$ and becomes 3${\mathit{d}}^{5}$L (where L denotes a ligand hole) in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ series for low Sr concentration. The main component of the ground state of ${\mathrm{LaMnO}}_{3}$ is 3${\mathit{d}}^{4}$ and becomes a mixture of 3${\mathit{d}}^{3}$ and 3${\mathit{d}}^{4}$L in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ series. The trends in controlled- valence properties of similar oxides across the transition-metal series can be rationalized within the framework of the Zaanen-Sawatzky-Allen model.

The colour hexagon: a chromaticity diagram based on photoreceptor excitations as a generalized representation of colour opponency

Abstract: A chromaticity diagram which plots the 3 photoreceptor excitations of trichromatic colour vision systems at an angle of 120° is presented. It takes into acount the nonlinear transduction process in the receptors. The resulting diagram has the outline of an equilateral hexagon. It is demonstrated by geometrical means that excitation values for any type of spectrally opponent mechanism can be read from this diagram if the weighting factors of this mechanism add up to zero. Thus, it may also be regarded as a general representation of colour opponent relations, linking graphically the Young-Helmholtz theory of trichromacy and Hering's concept of opponent colours. It is shown on a geometrical. basis that chromaticity can be coded unequivocally by any two combined spectrally opponent mechanisms, the main difference between particular mechanisms being the extension and compression of certain spectral areas. This type of graphical representation can qualitatively explain the Bezold-Brucke phenomenon. Furthermore, colour hexagon distances may be taken as standardized perceptual colour distance values for trichromatic insects, as is demonstrated by comparison with behavioural colour discrimination data of 3 hymenopteran species.

Multinomial logistic regression algorithm

Abstract: The lower bound principle (introduced in Bohning and Lindsay 1988, Ann. Inst. Statist. Math., 40, 641–663), Bohning (1989, Biometrika, 76, 375–383) consists of replacing the second derivative matrix by a global lower bound in the Loewner ordering. This bound is used in the Newton-Raphson iteration instead of the Hessian matrix leading to a monotonically converging sequence of iterates. Here, we apply this principle to the multinomial logistic regression model, where it becomes specifically attractive.

Assembly and function of the two ABC transporter proteins encoded in the human major histocompatibility complex.

Abstract: Presentation of cytoplasmic antigens to class I-restricted cytotoxic T cells implied the existence of a specialized peptide transporter. For most class I heavy chains, association with peptides of the appropriate length is required for stable assembly with beta 2-microglobulin. Mutant cells RMA-S and .174/T2 neither assemble stable class I molecules nor present intracellular antigens, and we have suggested that they have lost a function required for the transport of short peptides from the cytosol to the endoplasmic reticulum. The genetic defect in .174 has been localized to a large deletion in the class II region of the major histocompatibility complex, within which two genes (RING4 and RING11) have been identified that code for 'ABC' (ATP-binding cassette) transporters. We report here that the protein products of these two genes assemble to form a complex. Defects in either protein result in the formation of unstable class I molecules and loss of presentation of intracellular antigens. The molecular defect in a new mutant, BM36.1, is shown to be in the ATP-binding domain of the RING11/PSF2 protein. This is in contrast to the mutant .134, which lacks the RING4/PSF1 protein.

Role of octreotide in the prevention of postoperative complications following pancreatic resection.

Abstract: Though morbidity and mortality rates following pancreatic resection have improved in recent years, they are still around 35% and 5%, respectively. Typical complications, such as pancreatic fistula, abscess, and subsequent sepsis, are chiefly associated with exocrine pancreatic secretion. In order to clarify whether the perioperative inhibition of exocrine pancreatic secretion prevents complications, we assessed the efficacy of octreotide, a long-acting somatostatin analogue. We conducted a randomized, double-blind, placebo-controlled, multicenter trial in 246 patients undergoing major elective pancreatic surgery. Patients were stratified into a high-risk stratum (limited to patients with pancreatic and periampullary tumors) or low-risk stratum (patients with chronic pancreatitis). Patients received octreotide (3 x 100 micrograms) or placebo subcutaneously for 7 days perioperatively. Eleven complications were defined: death, leakage of anastomosis, pancreatic fistula, abscess, fluid collection, shock, sepsis, bleeding, pulmonary insufficiency, renal insufficiency, and postoperative pancreatitis. Two hundred patients underwent pancreatic head resection, 31 patients underwent left resection, and 15 patients had other procedures. The overall mortality rate within 90 days was 4.5%, with 3.2% in the octreotide group and 5.8% in the placebo group. The complication rate was 32% in the patients receiving octreotide (40 of 125 patients) and 55% in patients receiving placebo (67 of 121 patients) (p less than 0.005). In the patients in the high-risk stratum, complications were observed in 26 of the 68 (38%) patients treated with octreotide and in 46 of 71 (65%) patients given placebo (p less than 0.01). Whereas in patients in the low-risk stratum, the complication rate was 25% (14 of 57 patients) in those treated with octreotide and 42% (21 of 50 patients) in patients given placebo (p = NS). The perioperative application of octreotide reduces the occurrence of typical postoperative complications after pancreatic resection, particularly in patients with tumors.

Full correction of the self-absorption in soft-fluorescence extended x-ray-absorption fine structure.

Abstract: The amplitude of the extended x-ray-absorption fine structure of concentrated samples measured in the fluorescence mode (FLEXAFS) as well as the overall shape of the fluorescence-yield spectra strongly depend on the detection geometry through the self-absorption effect. In these cases, a conventional EXAFS analysis can lead to systematic errors in the determination of physical parameters. We studied the distortions in the FLEXAFS spectra through the self-absorption effect measuring the FLEXAFS of a NiO single crystal above the oxygen K edge for various detection geometries. We show that knowing the stoichiometry of the sample we can fully correct for the self-absorption effect using a simple theory and obtain the correct, geometry-independent oxygen EXAFS of NiO. The correction procedure presented here for the prototype system of NiO is generally applicable and should be the first step in the analysis of FLEXAFS data of concentrated samples. We calculate the information depth of the fluorescence detection as a function of the experimental geometry. The knowledge of the self-absorption in relationship to the information depth allows the determination of the optimum experimental setup.

Different β-subunits determine G-protein interaction with transmembrane receptors

Abstract: REGULATORY GTP-binding proteins (G proteins) are membrane-attached heterotrimers (α, β, γ) that mediate cellular responses to a wide variety of extracellular stimuli1,2. They undergo a cycle of guanine-nucleotide exchange and GTP hydrolysis, during which they dissociate into αsubunit and βγ complex1. The roles of G-protein αsubunits in these processes and for the specificity of signal transduction are largely established; the α- and γ-subunits are essential for receptor-induced G-protein activation and seem to be less diverse and less specific. Although the complementary DNAs for several β-subunits have been cloned2,5–8, isolated sub-units have only been studied as βγ complexes3,9–12. Functional differences have been ascribed to the γ-subunit on the basis of extensive sequence similarity among β-subunits and apparent heterogeneity in γ-subunit sequences13,14.βγ complexes can interact directly or indirectly with different effectors10,11,15–20. They seem to be interchangeable in their interaction with pertussis toxinsensitive α-subunits3, so we tested this by microinjecting antisense oligonucleotides into nuclei of a rat pituitary cell line to suppress the synthesis of individual β-subunits selectively. Here we show that two out of four subtypes of β-subunits tested (β1 and β3) are selectively involved in the signal transduction cascades from muscarinic M4 (ref. 4) and somatostatin receptors, respectively, to voltage-dependent Ca2+ channels.

The evolutionary adaptation of flower colours and the insect pollinators' colour vision

Abstract: The evolutionary tuning between floral colouration and the colour vision of flower-visiting Hymenoptera is quantified by evaluating the informational transfer from the signalling flower to the perceiving pollinator. The analysis of 180 spectral reflection spectra of angiosperm blossoms reveals that sharp steps occur precisely at those wavelengths where the pollinators are most sensitive to spectral differences. Straight-forward model calculations determine the optimal set of 3 spectral photoreceptor types for discrimination of floral colour signals on the basis of perceptual difference values. The results show good agreement with the sets of photoreceptors characterized electrophysiologically in 40 species of Hymenoptera.

Medium-range order in glasses: Comparison of Raman and diffraction measurements.

Abstract: The correlation lengths of vitreous structures estimated from the low-frequency (boson) peak in Raman spectra and from the width of the first sharp diffraction peak are compared. This first comparison shows that the two estimates, which are based on dynamic and static properties, respectively, are in good quantitative agreement. The present result supports the concepts that (a) a decisive scale for structural order in glasses is \ensuremath{\sim}10 \AA{}, and (b) the low-frequency excitations are defined by the characteristic length in vitreous structures.

Facial expression and emotional face recognition in schizophrenia and depression

Abstract: Twenty-three acute schizophrenics, 21 acute major depressives (Research Diagnostic Criteria), and 15 normal controls participated in a study on facial expression and emotional face recognition. Under clinical conditions, spontaneous facial expression was assessed according to the affective flattening section of the Scale for the Assessment of Negative Symptoms. Under experimental laboratory conditions involuntary (emotion-eliciting interview) and voluntary facial expression (imitation and simulation of six basic emotions) were recorded on videotape, from which a raterbased analysis of intensity or correctness of facial activity was obtained. Emotional face recognition was also assessed under experimental conditions using the same stimulus material. All subjects were assessed twice (within 4 weeks), controlling for change of the psychopathological status in the patient groups. In schizophrenics, neuroleptic drug influence was controlled by random allocation to treatment with either haloperidol or perazine. The main findings were that schizophrenics and depressives are characterized by different quantitative, qualitative, and temporal patterns of affect-related dysfunctions. In particular, schizophrenics demonstrated a trait-like deficit in affect recognition and in their spontaneous and voluntary facial activity, irrespective of medication, drug type and dosage, or extrapyramidal side-effects. In depressives a stable deficit could be demonstrated only in their involuntary expression under emotion-eliciting interview conditions, whereas in the postacute phase a reduction in their voluntary expression became apparent. Differences in patterns of affect-related behavioral deficits may reflect dysfunctions in different underlying psychobiological systems.

Multilevel preconditioning

Abstract: This paper is concerned with multilevel techniques for preconditioning linear systems arising from Galerkin methods for elliptic boundary value problems. A general estimate is derived which is based on the characterization of Besov spaces in terms of weighted sequence norms related to corresponding multilevel expansions. The result brings out clearly how the various ingredients of a typical multilevel setting affect the growth rate of the condition numbers. In particular, our analysis indicates how to realize even uniformly bounded condition numbers. For example, the general results are used to show that the Bramble-Pasciak-Xu preconditioner for piecewise linear finite elements gives rise to uniformly bounded condition numbers even when the refinements of the underlying triangulations are highly nonuniform. Furthermore, they are applied to a general multivariate setting of refinable shift-invariant spaces, in particular, covering those induced by various types of wavelets.

Dimensional crossover in ultrathin Ni(111) films on W(110).

Abstract: IIn situR magnetic resonance measurements of ultrathin Ni(111) on W(110) prepared in ultrahigh vacuum have been carried out to determine the thickness dependence of the critical exponent \ensuremath{\beta} and the Curie temperature ${\mathit{T}}_{\mathit{c}}$. We find that \ensuremath{\beta} changes drastically from 0.30 to 0.13 between 7 and 5 monolayers. We attribute this behavior to a crossover from a three- to a two-dimensional magnetic behavior. The observed ${\mathit{T}}_{\mathit{c}}$'s and linewidths also exhibit the effect of the dimensional crossover. Ni films \ensuremath{\le}4 layers thick show a truly two-dimensional magnetic phase transition with \ensuremath{\beta}=0.13.

Climate anomalies in Europe associated with ENSO extremes

Abstract: Surface pressure, temperature and precipitation anomalies in Europe are composed for the El Nino-Southern Oscillation (ENSO) warm and cold extremes. During warm event winters, negative pressure departures at western and central European stations are associated with positive temperature and precipitation anomalies; the reverse signals are observed in northern Europe. During cold episodes the field of negative pressure deviations is shifted northward with positive temperature and precipitation anomalies, whereas higher pressure is observed over central Europe. This shift of the anomalies corresponds to a shift in the dominating cyclone track (deduced from weather maps), which may be interpreted as the response of the (sensitive tail end of the) cross-Atlantic storm track on the high-pressure anomalies occurring at times in the northern or central part of the North Atlantic/European sector during warm or cold ENSO winters, respectively.

Stratospheric temperature increases due to Pinatubo aerosols

Abstract: Northern-Hemisphere stratospheric temperatures at 30 and 50 mb beginning in June 1991 are compared with 20-year (1965-1984) and 26-year (1964-1989) monthly means. Significant temperature increases are shown in July, August, September, and October for latitudes from approximately 30 deg N to the equator. In September and October deviations are observed for large areas between the equator and 30 deg N, with temperature increases as high as + 3.5 C occurring at some locations. The monthly averaged zonal mean 30-mb temperatures at 20 deg N in September and October were approximately 2.5 C higher that the 26-year mean, with some daily zonal mean increases of almost 3 C. Higher values occurred equatorward of 20 deg N. These warmings are due to absorption of radiation by the aerosols produced from the June eruptions of the volcano Pinatubo (15.1 deg N, 120.4 deg E) in the Philippines. Stratospheric warmings are expected to be occurring simultaneously at southern latitudes, especially from the equator to about 20 deg S, based on satellite and lidar measurements of the locations of the new aerosol layers. These localized temperature increases should decrease in magnitude and become more global as the cloud disperses globally and spreads in altitude.

Follicular dendritic cells are a major reservoir for human immunodeficiency virus type 1 in lymphoid tissues facilitating infection of CD4+ T-helper cells.

Abstract: Human immunodeficiency virus type 1 (HIV-1) infection causes progressive depletion of CD4/HIV-receptor-positive T helper lymphocytes, ultimately leading to AIDS. The major HIV reservoir and site of T-helper cell infection in lymphoid tissues, however, has remained poorly defined. The authors used in situ hybridization in combination with immunohistologic labeling techniques to identify the phenotype of HIV-infected cells in lymph nodes from patients at different stages of HIV-infection. The number of HIV-infected macrophages, widely considered the major site of HIV replication, was extremely low. There was no evidence for HIV-infection of endothelial and interdigitating reticulum cells. However, HIV RNA was found in small but consistent proportions of CD45RO-positive T cells and in the vast majority of follicular dendritic cells (FDC) in a pattern suggestive of active infection in addition to HIV-immunocomplex trapping on cell membranes. FDC may therefore be a major HIV reservoir and since T-helper cells travel through the FDC meshwork during their migration within lymphoreticular tissues, it appears likely that HIV-replicating T cells may infect FDC, which then infect new T cells, thus causing a gradual dissemination of the virus to all FDC and thereby a steadily increasing infection of T-helper/memory cells within germinal centers. This results in CD4+ T cell depletion, and ultimately, in immunodeficiency.

Cortico-cortical connections and cytoarchitectonics of the primate vestibular cortex: A study in squirrel monkeys (Saimiri sciureus)

Abstract: The cortical connections of two vestibular fields [parieto-insular vestibular cortex (PIVC) and area 3aV] were studied in the squirrel monkey (Saimiri sciureus) by means of retrograde tracer techniques. Small iontophoretic or pressure injections of horseradish peroxidase (HRP), wheat-germ-HRP, Nuclear Yellow, and Fast Blue were administered to the cytoarchitectonic areas Ri (PIVC), 3aV, the parieto-temporal association area T3, the granular insula (Ig), and the rostral part of area 7 (7ant). The injection sites were physiologically characterized by means of microelectrode recordings and vestibular, optokinetic, or somatosensory stimulation: Area Ri is the region of the parieto-insular vestibular cortex (PIVC) as defined in macaques. The neck-trunk region of area 3a (area 3aV) also contains many neurons responding to stimulation of semicircular canal receptors. Some neurons of area T3 bordering on the PIVC also receive vestibular signals, but most neurons in area T3 responded preferentially to large-field optokinetic stimulation and not to vestibular stimulation. In none of the areas mentioned were responses to otolith stimulation found. The PIVC receives inputs from frontal and parietal cortical areas, especially areas 8a, 6, 3a, 3aV, 2, and 7ant. Area T3 receives signals from the insular and retroinsular cortex, various parts of area 7, visual areas of the parieto-occipital and parieto-temporal regions (area 19) and from a sector of the upper bank of the temporal sulcus (STS-area). The cortical afferents to area 3aV stem from areas 24, 4, 6, 7ant, from other parts of the primary somatosensory cortex, the secondary somatosensory cortex (SII), the retroinsular cortex (Ri), and the granular insula (Ig). In the border region of the areas 2 and 7ant, labelled neurons appeared after injections into both the PIVC and the area 3aV. This region is presumably the homologue to the vestibular area 2v of the macaque brain. In all regions cells within the contralateral cortex were less frequently labelled than cells in the homologous structures of the ipsilateral hemisphere. The cortical system for processing vestibular information about head-in-space movement consists mainly of the reciprocally interconnected areas PIVC and 3aV, and most likely of border regions of area 2 and 7ant. This "inner cortical vestibular circuit" also receives signals from two other cortical sensory systems, the somatosensory-proprioceptive system mediated by the primary somatosensory cortex and the visual movement system (optokinetic or visual flow signals). These visual movement signals reach PIVC via area 19 and area T3.(ABSTRACT TRUNCATED AT 400 WORDS)

A Combinatorial Bound for Linear Programming and Related Problems

Abstract: We present a simple randomized algorithm which solves linear programs with n constraints and d variables in expected O(d32 d n) time. The expectation is over the internal randomizations performed by the algorithm, and holds for any input.

Nitric oxide synthetase (NOS)-containing sympathoadrenal cholinergic neurons of the rat IML-cell column: evidence from histochemistry, immunohistochemistry, and retrograde labeling.

Abstract: Nitric oxide synthetase (NOS) can be selectively stained in neurons by either NAJIPHdiaphorase (i.e., NOS)-histochemistry or immunohistochemistry with antibodies raised against NOS, which apparently label identical reactive sites (Hope, B.T., G.J. Michael, K.M. Knigge, and S.R. Vincent, Proc. Natl. Acad. Sci. USA 88:2811-2814, '91). We provide histochemical evidence for the existence of a neuron-specific NOS-activity in autonomic neurons of the thoracic spinal cord. Among the four main preganglionic cell clusters investigated at midthoracic levels, Th7-10, the intermediolateral (1ML)-cell column was the most prominently stained cell group. The histochemical staining was absent in other spinal cord neurons and non-neuronal cells, e.g., GFAP-positive glial cells. Staining was completely blocked by ""-nitroL-arginine (L-"A), a potent NOS-inhibitor for brain and peripheral autonomic neurons, but was still observed in the presence of another NOS-inhibitor, Nu-monomethyl-L-arginine (MeArg). The NOS-activity co-localized with nearly half of the ChAT-immunostained neurons located in the mid-thoracic IML-cell column as quantified by cell counts in single and double-stained tissue sections. We conclude that NOS-activity-containing neurons represent a distinct group among cholinergic IML-neurons, which suggests a more general function of this newly defined subpopulation of the spinal cord autonomic system. In vivo Fast blue retrograde labeling combined with histochemical staining and immunostaining revealed that sympathoadrenal projection neurons belong to the distinct NOS and ChAT-positive IML-cell group. The results are consistent with the idea of a crucial role of NOS and the related L-argininedependent nitric oxide biosynthesis for adrenomedullary innervation and autonomic control of adrenal gland function. In the adult rat, the intermediate region of the thoracic spinal cord (comprising laminae VI, VII, and X according to the classification of Rexed, '54) contains sympathetic preganglionic neurons (SPNs) that form distinct cholinergic cell clusters (Navaratnam and Lewis, '70; Borges and Iversen, '86) and are referred to as the central autonomic (CA),

Borna disease virus, a negative-strand RNA virus, transcribes in the nucleus of infected cells.

Abstract: Borna disease virus, an unclassified infectious agent, causes immune-mediated neurologic disease in a wide variety of animal hosts and may be involved in pathogenesis of selected neuropsychiatric diseases in man. Initial reports suggested that Borna disease virus is a single-stranded RNA virus. We describe here a method for isolation of viral particles that has allowed definitive identification of the genome as containing a negative-polarity RNA. Further, we show that the viral mRNAs are transcribed in the nucleus.

Event related potentials and EEG components in a semantic memory search task.

Abstract: This study examined the effects of memory search and related processes on both time and frequency domain components of electroencephalographic activity More specifically, we were interested in the relationship between EEG and event-related potential (ERP) components as a function of memory load and response type Subjects performed a semantic memory search task in which they matched word probes to category labels Consistent with previous studies, reaction time increased and accuracy decreased with increasing memory loads A negative component of the ERP (N400) was found to reflect semantic mismatch: N400s were larger for the nontargets than for the targets Two ERP components were found to be reciprocally related to memory load P300 decreased and Negative Slow Wave increased in amplitude with increases in the size of the memory set These two ERP components were reflected by different components in a Principal Components Analysis The power in the theta band (5-7 Hz) also increased as a function of memory load and appears to be functionally and topographically related to the Negative Slow Wave in the ERP It is argued that both measures are jointly determined and reflect the difficulty of the conceptual operations during memory search

CzcR and CzcD, gene products affecting regulation of resistance to cobalt, zinc, and cadmium (czc system) in Alcaligenes eutrophus

Abstract: The czcR gene, one of the two control genes responsible for induction of resistance to Co2+, Zn2+, and Cd2+ (czc system) in the Alcaligenes eutrophus plasmid pMOL30, was cloned and characterized. The 1,376-bp sequence upstream of the czcCBAD structural genes encodes a 41.4-kDa protein, the czcR gene product, transcribed in the opposite direction of that of the czcCBAD genes. The putative CzcR polypeptide (355 amino acid residues) contains 11 cysteine and 14 histidine residues which might form metal cation-binding sites. A czcC::lacZ reporter gene translational fusion was constructed, inserted into plasmid pMOL30 in A. eutrophus, and expressed under the control of CzcR. Zn2+, Co2+, and Cd2+, as well as Ni2+, Cu2+, Hg2+, and Mn2+ and even Al3+, served as inducers of beta-galactosidase activity. Besides the CzcR protein, the membrane-bound CzcD protein was essential for induction of czc. The CzcR and CzcD proteins display no sequence similarity to two-component regulatory systems of a sensor and a response activator type; however, CzcD has 34% identity with the ZRC-1 protein, which mediates zinc resistance in Saccharomyces cerevisiae (A. Kamizomo, M. Nishizawa, Y. Teranishi, K. Murata, and A. Kimura, Mol. Gen. Genet. 219:161-167, 1989).