Aphid transmission of beet western yellows luteovirus requires the minor capsid read-through protein P74.

Beet western yellows luteovirus is obligately transmitted by the aphid Myzus persicae in a circulative, non-propagative fashion. Virus movement across the epithelial cells of the digestive tube into the hemocoel and from the hemocoel into the accessory salivary glands is believed to occur by receptor-mediated endocytosis and exocytosis. Virions contain two types of protein; the major 22 kDa capsid protein and the minor read-through protein, P74, which is composed of the major capsid protein fused by translational read-through to a long C-terminal extension called the read-through domain. Beet western yellows virus carrying various mutations in the read-through domain was tested for its ability to be transmitted to test plants by aphids fed on agro-infected plants and semi-purified or purified virus preparations. The results establish that the read-through domain carries determinants that are essential for aphid transmission. The findings also reveal that the read-through domain is important for accumulation of the virus in agro-infected plants.     

Laminin decreases PRL and IGFBP-1 expression during in vitro decidualization of human endometrial stromal cells

The expression of laminin, a major constituent of endometrial cell basement membranes, is increased during differentiation of human endometrial stromal cells (decidualization). To determine whether laminin plays a role in decidualization, we studied the effects of laminin substrate on the synthesis and release of prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1), two major secretory proteins of decidualized stromal cells. Endometrial stromal cells were plated on laminin as well as several other extracellular matrix (ECM) proteins (types 1 and IV collagen or fibronectin) and on plastic, and cultured in media containing medroxyprogesterone acetate (MPA) and estradiol. Cells cultured on plastic or ECM proteins displayed similar morphological changes indicative of decidualization. However, the release of PRL and IGFBP-1 from cells cultured on plastic and ECM proteins (types 1 and IV collagen and fibronection) was approximately 2.1-fold and 2.8-fold greater respectively, than from cells cultured on laminin. The decrease in PRL and IGFBP-1 expression in cells cultured on laminin was not due to differences in initial cell attachment efficiency or final DNA content. In addition, laminin had no effect on the content of laminin protein or fibronectin mRNA levels, indicating that the effects of laminin on PRL and IGFBP-1 were specific. PGE₂ stimulated the release of PRL and IGFBP-1 from cells cultured on laminin to levels comparable to those from cells cultured on plastic or other ECM proteins. This indicates that the decrease in PRL and IGFBP-1 release by laminin was not due to a generalized unresponsiveness. In contrast to the effects of laminin during decidualization, PRL expression was not altered by laminin in terminally differentiated decidual cells isolated at term. Our results support a role for laminin in selectively regulating PRL and IGFBP-1 gene expression during in vitro decidualization of human endometrial stromal cells. © 1995 Wiley-Liss, Inc.     

Role of the active-site cysteine of Pseudomonas aeruginosa azurin. Crystal structure analysis of the CuII(Cys112Asp) protein

Replacement of the cysteine at position 112 of Pseudomonas aeruginosa azurin with an aspartic acid residue results in a mutant (Cys112Asp) protein that retains a strong copper-binding site. Cu^II(Cys112Asp) azurin can be reduced by excess [Ru^II(NH₃)₆]²⁺, resulting in a Cu^I protein with an electronic absorption spectrum very similar to that of wild-type Cu^I azurin. Cys112Asp azurin exhibits reversible interprotein electron-transfer reactivity with P. aeruginosa cytochrome c ₅₅₁ (μ?=?0.1?M sodium phosphate (pH?7.0);E°(Cu^II/I)?=?180 mV vs NHE); this redox activity indicates that electrons can still enter and exit the protein through the partially solvent-exposed imidazole ring of His117. The structure of Cu^II(Cys112Asp) azurin at 2.4-Å resolution shows that the active-site copper is five coordinate: the pseudo-square base of the distorted square-pyramidal structure is defined by the imidazole N^δ atoms of His46 and His117 and the oxygen atoms of an asymmetrically-bound bidentate carboxylate group of Asp112; the apical position is occupied by the oxygen atom of the backbone carbonyl group of Gly45. The Cu^II–Asp112 interaction is distinguished by an approximately 1.2-Å displacement of the metal center from the plane defined by the Asp112 carboxylate group.     

General practitioners' perceptions of the tolerability of antidepressant drugs: a comparison of selective serotonin reuptake inhibitors and tricyclic antidepressants.

OBJECTIVE: To examine inceptions and discontinuations of antidepressants in general practice. DESIGN: An observational study analysing data from an ongoing cross sectional postal survey. Every three months a representative sample of 250 doctors recorded prescribing activity for four weeks. This provided 4000 general practitioner weeks of recording per year. SETTING: A representative panel of general practitioners in England, Wales, and Scotland. SUBJECTS: Patients who began a new course of an antidepressant or had their treatment stopped or changed by the general practitioner between 1 July 1990 and 30 June 1995. MAIN OUTCOME MEASURES: Numbers of patients prescribed a new course of antidepressant; numbers discontinuing treatment; the ratio of antidepressant discontinuations to antidepressant inceptions; reasons for discontinuation; proportion of switches to another antidepressant. RESULTS: There were 13,619 inceptions and 3934 discontinuations of selective serotonin reuptake inhibitors and tricyclic antidepressants during the study. The number of newly prescribed courses of antidepressants increased by 116%, mostly due to an increase in prescribing of serotonin reuptake inhibitors. The ratio of total discontinuations to inceptions was significantly lower for serotonin reuptake inhibitors (22%) than for tricyclic antidepressants (33%). Differences persisted when controlled for age and sex of patients and severity of depression. However, there was more switching away from selective serotonin reuptake inhibitors when they failed (72%) than from tricyclic antidepressants (58%). CONCLUSIONS: Selective serotonin reuptake inhibitors are less likely than tricyclic antidepressants to be discontinued. A prospective study is needed in general practice to assess the implications of differences in discontinuation rates and switches on clinical and economic outcomes.     

ATPase and phosphatase activities from human red cell membranes III. Stimulation of K+-activated phosphatase by phospholipase C

Summary Treatment of red cell membranes with pure phospholipase C inactivates (Na⁺+K⁺)-ATPase activity and Na⁺-dependent phosphorylation but increases K⁺-dependent phosphatase activity. When phospholipase A₂ replaces phospholipase C, all activities are lost. Activation of K⁺-dependent phosphatase by treatment with phospholipase C is caused by an increase in the maximum rate of hydrolysis ofp-nitrophenylphosphate and in the maximum activating effect of K⁺, the apparent affinities for substrate and cofactors being little affected. After phospholipase C treatment K⁺-dependent phosphatase is no longer sensitive to ouabain but becomes more sensitive to N-ethylmaleimide. In treated membranes Na⁺ partially replaces K⁺ as an activator of the phosphatase. Although ATP still inhibits phosphatase activity, neither ATP nor ATP+Na⁺ are able to modify the apparent affinity for K⁺ of K⁺-dependent phosphatase in these membranes.     

Kinetics of assembly of a parvovirus, minute virus of mice, in synchronized rat brain cells

The rates of assembly of the three classes of particles of minute virus of mice were examined in synchronized rat brain cells by a combination of electron microscopy and biochemical techniques. We observed a burst of virus assembly beginning about 8 h after the end of cellular S phase. Labeled thymidine incorporated into the 1.46 g/cm3 class of full virus particles was transferred almost quantitatively to the 1.42 g/cm3 class. The 1.46 g/cm3 virus appeared to be an immediate precursor to the 1.42 g/cm3 class. Conversion of the 1.46 density virus to the 1.42 density particles was observed at the time of virus assembly. The processing was rapid and occurred primarily in the nucleus. Infected cells did not contain significant pools of viral DNA in a form that could be encapsulated in the absence of DNA synthesis. The role of the empty virus capsids in the assembly process is discussed.     

Re-evaluation of proposed C4 photosynthetic characteristics in the genus Larix

It has been suggested previously that Japanese larch ( Larix kaempferi ) exhibits characteristics of C₄ photosynthesis. To further evaluate this suggestion, stable carbon isotope ratios were determined for leaf and bark tissue of Larix gmelini, L. kaempferi, L. laricina, L. Iyallii, L. occidentalis , and L. sibirica. All δ¹³C values were more negative than –22‰. Short-term labeling with ¹⁴CO₂ showed that phosphoglyceric acid and other phosphorylated compounds were the first products of photosynthesis in L. sibirica. Both of these results strongly suggest that the initial fixation of atmospheric CO₂ in these six Larix species is accomplished solely via the C₃ photosynthetic pathway.     

Surface membrane redistribution and stabilization of concanavalin A-specific receptors following Yaba tumor poxvirus infection

Monkey kidney cells productively infected with Yaba tumor poxvirus clearly exhibit plasma membrane alterations when treated with both fluorescein-labeled and unlabeled concanavalin A. The convanavalin A-mediated cytoagglutination reaction for Yaba-infected Jinet and CV-1 cells increased linearly from 12 to 16 h post-infection, reaching a maximum by 24-28 h. Treatment of either Yaba-infected CVC-1 or Jinet cells with methyl-D-glucopyranoside before or after addition of concanavalin A completely blocked or reversed the cytoaglutination response. Trypsin treatment of uninfected CV-1 or Jinet cells enhanced concanavalin A-mediated cytoagglutination properties. Conversely, trypsin treatment of Yaba-infected Jinet cells resulted in a reduced cytoagglutination response. Increasing temperature and lectin concentration enhance concanavalin A-mediated cytoagglutination for uninfected, trypsin-treated and Yaba-infected CV-1 cells. Cytosine arabinoside has little or no effect on the Yaba-induced cell cytoagglutination reaction while cycloheximide blocks the cytoagglutinatin response if added prior to 12 h post-infection. Fluorescein-labeled concanavalin A binding studies have revealed that at 4 degrees C, Yaba-infected CV-1 cells display a predominantly 'patchy' pattern of topological fluorescence, while trypsin-treated and uninfected CV-1 cells at 4 degrees C display a uniform pattern of fluorescence binding. Patchy fluorescence, indicative of concanavalin A-suspeptible, receptor-site clustering on the surface membrane, was reduced 50% if Yaba-infected CV-1 cells were treated with glutaraldehyde (2.5%) before addition of fluorescein-labeled concanavalin A at 4 degrees C. Similar pre-fixatin of trypsin-treated CV-1 cells resulted in uniform, fluorescent labelling patterns at all assay temperatures.