Opposite fates of the purine metabolite allantoin under water and nitrogen limitations in bread wheat

Plant Molecular Biology - Degradation of nitrogen-rich purines is tightly and oppositely regulated under drought and low nitrogen supply in bread wheat. Allantoin is a key target metabolite for...     

Construction and structure studies of DNA-bipyridine complexes as versatile scaffolds for site-specific incorporation of metal ions into DNA

The facile construction of metal–DNA complexes using ‘Click’ reactions is reported here. A series of 2′-propargyl-modified DNA oligonucleotides were initially synthesized as structure scaffolds and were then modified through ‘Click’ reaction to incorporate a bipyridine ligand equipped with an azido group. These metal chelating ligands can be placed in the DNA context in site-specific fashion to provide versatile templates for binding various metal ions, which are exchangeable using a simple EDTA washing-and-filtration step. The constructed metal–DNA complexes were found to be thermally stable. Their structures were explored by solving a crystal structure of a propargyl-modified DNA duplex and installing the bipyridine ligands by molecular modeling and simulation. These metal–DNA complexes could have wide applications as novel organometallic catalysts, artificial ribonucleases, and potential metal delivery systems.     

Mate Choice in Captive American Kestrels,Falco sparverius,Parasitized by a Nematode,Trichinella pseudospiralis

The American kestrel (Falco sparverius) — Trichinella pseudospiralis host-parasite association was used as a laboratory model to study the effect of a nematode infection on (1) mate choice of female kestrels and (2) competitive abilities of male kestrels during the breeding season. Females were given the opportunity to choose between infected and uninfected males. There was no significant difference in the proportion of females that chose uninfected (n = 18) over infected (n = 16) males. Eight of 11 competitions between infected and uninfected males exposed to a caged female and a nest box were dominated by uninfected males. Female kestrels seemed to base their choices on the intensity of display effort by the males; the experimental level of infection did not affect male courtship behaviour. Although T. pseudospiralis is known to debilitate American kestrels, parasitized males in mate-choice tests may have diverted energy from less important functions to court the females.     

A rapidly activating delayed rectifier K+ current regulates pacemaker activity in adult mouse sinoatrial node cells

We have investigated the physiological role of the "rapidly activating" delayed rectifier K+ current (IKr) in pacemaker activity in isolated sinoatrial node (SAN) myocytes and the expression of mouse ether-a-go-go (mERG) genes in the adult mouse SAN. In isolated, voltage-clamped SAN cells, outward currents evoked by depolarizing steps (greater than -40 mV) were strongly inhibited by the class III methanesulfonanilide compound E-4031 (1-2.5 microM), and the deactivation "tail" currents that occurred during repolarization to a membrane potential of -45 mV were completely blocked. E-4031-sensitive currents (IKr) reached a maximum at a membrane potential of -10 mV and showed pronounced inward rectification at more-positive membrane potentials. Activation of IKr occurred at -40 to 0 mV, with half-activation at about -24 mV. The contribution of IKr to action potential repolarization and diastolic depolarization was estimated by determining the E-4031-sensitive current evoked during voltage clamp with a simulated mouse SAN action potential. IKr reached its peak value (approximately 0.6 pA/pF) near -25 mV, close to the midpoint of the repolarization phase of the simulated action potential, and deactivated almost completely during the diastolic interval. E-4031 (1 microM) slowed the spontaneous pacing rate of Langendorff-perfused, isolated adult mouse hearts by an average of 36.5% (n = 5). Expression of mRNA corresponding to three isoforms coded by the mouse ERG1 gene (mERG1), mERG1a, mERG1a', and mERG1b, was consistently found in the SAN. Our data provide the first detailed characterization of IKr in adult mouse SAN cells, demonstrate that this current plays an important role in pacemaker activity, and indicate that multiple isoforms of mERG1 can contribute to native SAN IKr.     

Amplification of trial-to-trial response variability by neurons in visual cortex

The visual cortex responds to repeated presentations of the same stimulus with high variability. Because the firing mechanism is remarkably noiseless, the source of this variability is thought to lie in the membrane potential fluctuations that result from summated synaptic input. Here this hypothesis is tested through measurements of membrane potential during visual stimulation. Surprisingly, trial-to-trial variability of membrane potential is found to be low. The ratio of variance to mean is much lower for membrane potential than for firing rate. The high variability of firing rate is explained by the threshold present in the function that converts inputs into firing rates. Given an input with small, constant noise, this function produces a firing rate with a large variance that grows with the mean. This model is validated on responses recorded both intracellularly and extracellularly. In neurons of visual cortex, thus, a simple deterministic mechanism amplifies the low variability of summated synaptic inputs into the large variability of firing rate. The computational advantages provided by this amplification are not known.     

HMGB1 is an endogenous immune adjuvant released by necrotic cells

Immune responses against pathogens require that microbial components promote the activation of antigen-presenting cells (APCs). Autoimmune diseases and graft rejections occur in the absence of pathogens; in these conditions, endogenous molecules, the so-called 'innate adjuvants', activate APCs. Necrotic cells contain and release innate adjuvants; necrotic cells also release high-mobility group B1 protein (HMGB1), an abundant and conserved constituent of vertebrate nuclei. Here, we show that necrotic HMGB1(-/-) cells have a reduced ability to activate APCs, and HMGB1 blockade reduces the activation induced by necrotic wild-type cell supernatants. In vivo, HMGB1 enhances the primary antibody responses to soluble antigens and transforms poorly immunogenic apoptotic lymphoma cells into efficient vaccines.     

Cooperativity in two-state protein folding kinetics

We present a solvable model that predicts the folding kinetics of two-state proteins from their native structures. The model is based on conditional chain entropies. It assumes that folding processes are dominated by small-loop closure events that can be inferred from native structures. For CI2, the src SH3 domain, TNfn3, and protein L, the model reproduces two-state kinetics, and it predicts well the average Phi-values for secondary structures. The barrier to folding is the formation of predominantly local structures such as helices and hairpins, which are needed to bring nonlocal pairs of amino acids into contact.     

Mutations in human parainfluenza virus type 3 hemagglutinin-neuraminidase causing increased receptor binding activity and resistance to the transition state sialic acid analog 4-GU-DANA (Zanamivir)

Entry and fusion of human parainfluenza virus type 3 (HPF3) require the interaction of the viral hemagglutinin-neuraminidase (HN) glycoprotein with its sialic acid receptor. 4-GU-DANA, a potent inhibitor of influenza virus neuraminidase, inhibits not only HPF3 neuraminidase but also the receptor binding activity of HPF3 HN and thus its ability to promote attachment and fusion. We previously generated a 4-GU-DANA-resistant HPF3 virus variant (ZM1) with a markedly fusogenic plaque morphology that harbored two HN gene mutations resulting in amino acid alterations. The present study using cells that express the individual mutations of ZM1 HN shows that one of these mutations is responsible for the increases in receptor binding and neuraminidase activities as well as the diminished sensitivity of both activities to the inhibitory effect of 4-GU-DANA. To examine the hypothesis that increased receptor binding avidity underlies 4-GU-DANA resistance, parallel studies were carried out on the high-affinity HN variant virus C22 and cells expressing the C22 variant HN. This variant also exhibited reduced sensitivity to 4-GU-DANA in terms of receptor binding and infectivity but without concomitant changes in the neuraminidase activity of HN. Another high-affinity HN variant, C0, was not resistant in terms of infectivity; however, a small increase in the receptor binding activity of C0 HN and a partial resistance of this activity to 4-GU-DANA were revealed by sensitive methods that we developed. In each virus variant, one mutation in HN accounted for both increased receptor binding avidity and 4-GU-DANA resistance; the higher affinity for the receptor overcomes the inhibitory effect of 4-GU-DANA. Thus, in contrast to influenza viruses for which 4-GU-DANA escape variants include hemagglutinin mutants with decreased receptor binding avidity that promotes virion release, for HPF3, HN mutants with increased receptor binding avidity are those that can escape the growth inhibitory effect of 4-GU-DANA.     

Male rock sparrows adjust their breeding strategy according to female ornamentation: parental or mating investment?

We investigated the relations between female quality and ornamentation and between male breeding investment and female ornamentation in the rock sparrow, Petronia petronia, a passerine in which both sexes have a yellow breast patch. Breast patch size in females was positively correlated with body mass and breeding status; double-brooding and primary females of polygynous males had a larger patch, and patch size could therefore be an indicator of female phenotypic quality. We conducted a field experiment to test whether males allocate their parental effort in relation to female quality, as predicted by the differential allocation hypothesis. We increased and reduced the ornament sizes of paired females and compared the behaviour of their males before and after manipulation. Frequency of brood feeding by the male was not affected by female ornament manipulation; there was a nonsignificant trend for females with enlarged ornaments, contrary to predictions, to increase their feeding rate. Reducing female ornaments resulted in a decrease in male nest attendance, a measure of passive brood defence, whereas enlarging the ornament had no effect. Males concurrently reduced their territorial (song output) and sexual activity (courtship and copulation). The reduction in sexual activity suggests that males may have changed their nest attendance in response to their mate's renesting probability. Whatever the interpretation, these results provide some of the first evidence that not only female, but also male, birds change breeding strategy according to their mate's phenotype in the wild. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.