Nitrogen Oxyanion-dependent Dissociation of a Two-component Complex That Regulates Bacterial Nitrate Assimilation

Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression.     

Characterization of Senescence in Lemna gibba G3: A Determinate Growth System

Frond senescence in Lemna gibba G3 was characterized, and itscontrol by light, ABA and kinetin investigated. The plant exhibitsa determinate growth pattern with a frond producing a set numberof daughter fronds before undergoing senescence and death regardlessof whether or not it flowers. When a frond was cut in half,the distal half (half frond) which lacks any meristem underwentrapid senescence as compared with intact fronds. In both intactand half fronds, the onset of senescence was accelerated byABA and retarded by kinetin. Continuous white light acceleratedsenescence in both intact and half fronds over the dark controls.Under different photoperiodic light regime, the pace of daughterfrond production is accelerated in proportion to the lengthof light period. In half fronds, however, very short photoperiodiclight treatments (e.g. 1L: 23D or 3L: 21D) rather delayed senescenceover the dark controls. Two separate light control systems operatingin opposite directions in Lemana senescence appear to exist. ¹Present address: Department of Biology, Yonsei University,Seoul 120-749, Korea ²Present address: U.S. Department of Agriculture, Aero SpaceBuilding, Rm. 323, 901 D Street, S.W., Washington, D.C. 20251-2200, U.S.A. (Received July 13, 1989; Accepted May 8, 1990)     

EVIDENCE OF RELATIONSHIP BETWEEN EXTRA DIMINUTIVE CHROMOSOMES IN GEOGRAPHICALLY REMOTE RACES OF OENOTHERA

Cleland , R. E. (Indiana U., Bloomington), and B. B. Hyde . Evidence of relationship between extra diminutive chromosomes in geographically remote races of Oenothera. Amer. Jour. Bot. 50(2): 179–185. Illus. 1963.—Two California races of O. hookeri, Mono (from Mono Co.) and Mataguey (from San Diego Co.), have extra diminutive chromosomes. These diminutives do not associate with any of the normal chromosomes present. The extras from the 2 races, however, are able to synapse with each other and to form chiasmata, although the extras in Mono are distinctly larger than these in Mataguey. This suggests that they are at least partially homologous and that they have come from a common source. Two alternative hypotheses for their origin are suggested: (1) they have resulted from the loss of pairing ends through deletion, having descended from the same chromosome; (2) they represent normal chromosomes derived from another subgenus, through an inter-subgeneric cross followed by a backcross to hookeri. The facts tend to favor the latter hypothesis.     

Effect of incremental exercise on airway and systemic inflammation in patients with COPD

Airway and systemic inflammation are features of chronic obstructive pulmonary disease (COPD), and there is growing interest in clarifying the inflammatory processes. Strenuous exercise induces an intensified systemic inflammatory response in patients with COPD, but no study has investigated the airway inflammatory and anti-inflammatory responses to exercise. Twenty steroid-na?ve, ex-smokers with diagnosed COPD (forced expired volume in 1 s = 66 ± 12%) underwent baseline collection of venous blood and induced sputum followed by an incremental exercise test to symptom limitation 48 h later. Additional venous blood samples were collected following exercise at 0, 2, and 24 h, while induced sputum was collected 2 and 24 h after exercise. Sputum and blood samples were analyzed for differential cell count, CD4(+) and CD8(+) T lymphocytes (serum only), interleukin (IL)-6, IL-8, IL-10, chemokine (C-C motif) ligand 5 (CCL5), and high sensitivity C-reactive protein (serum only). There was an increase in the number of sputum eosinophils (cells/gram, P = 0.012) and a reduction in sputum IL-6 (P = 0.01) 24 h postexercise. Sputum IL-8 and CCL5 were also persistently decreased after exercise (P = 0.0098 and P = 0.0012, respectively), but sputum IL-10 did not change. There was a decrease in serum eosinophils 2 h after exercise (P = 0.0014) and a reduction in serum CCL5 immediately following and 2 h postexercise (P < 0.0001). Both serum eosinophils and CCL5 returned to baseline levels within 24 h. An acute bout of exercise resulted in a significant increase in the number of sputum eosinophils, which may be mediated by serum CCL5. However, there was also a reduction in sputum proinflammatory cytokines, suggesting some anti-inflammatory effect of exercise in the lungs of steroid-na?ve patients with COPD.     

Why aren't there more black football managers?

Abstract

The number of black and minority ethnic (BME) managers in English professional association football, or soccer, has been stable for nearly ten years: there are usually between two and four (out of a possible ninety two). Yet black players regularly make up more than a quarter of professional club squads. The reasons for this apparent under-representation are explored among 1,000 football fans, including players and ex-players, both white and BME. Opinions were solicited via an online research platform http://www.topfan.co.uk, designed and executed by the authors. The findings indicate 56 per cent of respondents believe racism operates at the executive levels of football, i.e. the boardroom. While some accuse club owners and directors of deliberate discrimination, most suspect a form of unwitting or institutional racism in which assumptions about black people's capacities are not analysed and challenged and so continue to circulate. Among the possible remedies to this is the American National Football League's Rooney Rule, which mandates BME candidates’ inclusion on shortlists for senior coaching positions. A third of participants in the research approved of this type of initiative. While black managers are scarce when compared to the number of black players in professional football, their presence is actually an accurate reflection of their number in the total British population. So is the dearth of black managers an under-representation?     

The assembly of a highly ordered component of the cell wall: The role of heritable factors and of physical structure

Summary An analysis has been made of the biogenesis of the highly ordered lattice structure which comprises an integral part of the cell wall of Chlamydomonas reinhardi. By examining mutants showing various wall defects, it has been shown that in some mutants lattice assembly will only occur in the presence of a particular kind of physical structure; in others the composition of the medium influences assembly. The role of a heritable factor in lattice assembly has also been demonstrated; after prolonged vegetative culture certain mutants lose the ability to form lattice, but regain this ability on passing through the diploid sexual phase. An attempt is made to integrate this information to provide a model for the control of assembly and inheritance of the wall.     

Instability of the growth-limiting proteins of the Avena coleoptile and their pool size in relation to auxin

Summary The stability and pool size of the growth-limiting proteins (GLP) of the Avena coleoptile have been studied by measuring the time required for cycloheximide to inhibit the growth of auxin-treated segments. Inhibition of growth follows inhibition of protein synthesis by 20–25 min regardless of the growth rate. This indicates that the growth inhibition is due to inherent instability of the GLP rather than to exhaustion of the pool through growth. A study of the amount and rate of auxin-induced growth which occurs when cycloheximide is added just before or after the auxin indicates that the rate of elongation is determined by the size of the GLP pool, and that the pool of GLP is low in the absence of auxin, but rapidly expands and reaches a maximum 20–25 min after addition of auxin. Three ways in which auxin might expand the pool of GLP are discussed.     

Rapid stimulation of K -H exchange by a plant growth hormone.

The growth-promoting phytotoxin fusicoccin¹ stimulates both [⁸⁶Rb⁺]K⁺ uptake and H⁺-excretion from oat coleoptiles by at least 5-fold after a lag of less than 90 seconds. Both processes are affected similarly by metabolic inhibitors and external pH. FC appears to activate a K⁺H⁺ exchange which is only partly specific for K⁺, and which can transport more H⁺ than K⁺. The natural plant growth hormone indoleacetic acid¹ also stimulates K⁺-uptake, but only after a long lag, and to a maximum of 30%, suggesting that IAA does not affect directly the K⁺H⁺ exchange process, and that the two hormones induce H⁺-excretion, and thus cell elongation, by different mechanisms.