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.     

Space use and genetic structure do not maintain color polymorphism in a species with alternative behavioral strategies

Space use including territoriality and spatial arrangement within a population can reveal important information on the nature, dynamics, and evolutionary maintenance of alternative strategies in color polymorphic species. Despite the prevalence of color polymorphic species as model systems in evolutionary biology, the interaction between space use and genetic structuring of morphs within populations has rarely been examined. Here, we assess the spatial and genetic structure of male throat color morphs within a population of the tawny dragon lizard, Ctenophorus decresii. Male color morphs do not differ in morphology but differ in aggressive and antipredator behaviors as well as androgen levels. Despite these behavioral and endocrine differences, we find that color morphs do not differ in territory size, with their spatial arrangement being essentially random with respect to each other. There were no differences in genetic diversity or relatedness between morphs; however, there was significant, albeit weak, genetic differentiation between morphs, which was unrelated to geographic distance between individuals. Our results indicate potential weak barriers to gene flow between some morphs, potentially due to nonrandom pre‐ or postcopulatory mate choice or postzygotic genetic incompatibilities. However, space use, spatial structure, and nonrandom mating do not appear to be primary mechanisms maintaining color polymorphism in this system, highlighting the complexity and variation in alternative strategies associated with color polymorphism.     

Ecosystem function and species loss – a microcosm study

There are too many kinds of organisms to be able to study and manage each, yet the loss of a single species can sometimes unravel an ecosystem. Such `fusewire species'– critical in the same sense that an electrical fuse can cut out a whole circuit – would be a rewarding focus for research and management effort. However, this approach can only be effective if these `fusewires' represent but a small proportion of the number of species in the system.  

Aim

To demonstrate methods for measuring what proportion of the species in a system are critical to ecosystem function.  

Methods

The prevalence of fusewire species was measured in manipulative experiments on an aquatic microcosm.  

Results

No single genus deletion caused changes in key characteristics of the system.  

Main conclusions

Comparison of these results with other published studies shows that the proportion of critical fusewire species varies amongst different ecosystems. The oxidation pond microcosms were shown to contain no single species indispensable to system function. They appear to be ill-suited to a management strategy which focuses on priority eukaryote species. However, a single study provides no evidence that this result is general or even typical of other kinds of ecosystems; it is presented here as an empirical model. Other methods of investigation are available; they are less experimentally rigorous but more practical. These could provide important guidance in planning an approach to management in a particular ecosystem.     

Regulation of meiotic recombination and prophase I progression in mammals.

Meiosis is the process by which diploid germ cells divide to produce haploid gametes for sexual reproduction. The process is highly conserved in eukaryotes, however the recent availability of mouse models for meiotic recombination has revealed surprising regulatory differences between simple unicellular organisms and those with increasingly complex genomes. Moreover, in these higher eukaryotes, the intervention of physiological and sex-specific factors may also influence how meiotic recombination and progression are monitored and regulated. This review will focus on the recent studies involving mouse mutants for meiosis, and will highlight important differences between traditional model systems for meiosis (such as yeast) and those involving more complex cellular, physiological and genetic criteria.     

book

Green Chemistry: Theory and Practice, by Paul T. Anastas and John C. Warner
Green Chemistry: Frontiers in Benign Chemical Synthesis and Processes, ed. by Paul T. Anastas and Tracy C. Williamson
Green Chemistry: Designing Chemistry for the Environment, ed. by Paul T. Anastas and Tracy C. Williamson     

Oligopeptide inhibitors of metalloendoprotease activity inhibit catecholamine secretion from bovine adrenal chromaffin cells by modulating intracellular calcium homeostasis

Synthetic oligopeptide inhibitors of metalloendoprotease activity were found to inhibit catecholamine release from intact bovine adrenal chromaffin cells. The efficiency of these compounds in blocking secretion was dependent on the type and dose of the secretagogues employed. By contrast, catecholamine release from digitonin-permeabilized cells stimulated with micromolar calcium was virtually not affected. Using a different model system mimicking protein-mediated membrane fusion during exocytosis (Bental, M., Lelkes, P.I., Scholma, J., Hoekstra, D., and Wilschut, J. (1984) Biochim. Biophys. Acta 774, 296-300) we found that exposure of chromaffin granules to a genuine metalloendoprotease, thermolysin, impaired their fusion competence with liposomes. The same oligopeptide inhibitors of metalloendoprotease activity that interfered with secretion from the intact cells were also found to cause an increase in 45Ca2+ efflux concomitant with a slight elevation of the free intracellular calcium concentration [( Ca2+]i) to levels not sufficient to elicit secretion. Subsequent stimulation of the cells in the presence of the potent inhibitors resulted in a reduced increase in the cytosolic calcium concentration, as compared to nontreated control cells. The reduction in the secretagogue-evoked rise in [Ca2+]i was also dependent on the time of pretreatment of the cells with the metalloendoprotease inhibitors. Consistently, none of these effects were seen with structurally similar oligopeptides that are not metalloendoprotease substrates/inhibitors. We conclude that potent inhibitors of metalloendoprotease activity and hence, presumably, the enzymes per se modulate stimulus-secretion coupling by interfering with calcium homeostasis rather than directly with membrane fusion.