Chiral supramolecular gold-cysteine nanoparticles: Chiroptical and nonlinear optical properties

Cysteine is a sulfur-containing amino acid that easily coordinates to soft metal ions and grafts to noble metal surfaces. We report a simple synthetic approach for the production of chiral gold-cysteine polymeric nanoparticles soluble in water. Conjugation of cysteine with gold in a polymeric way, leading to ~50 nm diameter nanoparticles, resulted in the generation of new characteristic circular dichroism (CD) signals in the region of 250–400 nm, whereas no CD signal changes were found with cysteine alone. We also investigate their nonlinear optical properties after two-photon absorption. Two-photon emission spectra and first hyper-polarizabilities, as obtained by the hyper-Rayleigh scattering technique, of these particles are presented.     

Crystal structure and biochemical characterization of the transmembrane PAP2 type phosphatidylglycerol phosphate phosphatase from <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Type 2 phosphatidic acid phosphatases (PAP2s) can be either soluble or integral membrane enzymes. In bacteria, integral membrane PAP2s play major roles in the metabolisms of glycerophospholipids, undecaprenyl-phosphate (C₅₅-P) lipid carrier and lipopolysaccharides. By in vivo functional experiments and biochemical characterization we show that the membrane PAP2 coded by the Bacillus subtilis yodM gene is the principal phosphatidylglycerol phosphate (PGP) phosphatase of B. subtilis. We also confirm that this enzyme, renamed bsPgpB, has a weaker activity on C₅₅-PP. Moreover, we solved the crystal structure of bsPgpB at 2.25 Å resolution, with tungstate (a phosphate analog) in the active site. The structure reveals two lipid chains in the active site vicinity, allowing for PGP substrate modeling and molecular dynamic simulation. Site-directed mutagenesis confirmed the residues important for substrate specificity, providing a basis for predicting the lipids preferentially dephosphorylated by membrane PAP2s.     

The CRISPR/Cas bacterial immune system cleaves bacteriophage and plasmid DNA

Bacteria and Archaea have developed several defence strategies against foreign nucleic acids such as viral genomes and plasmids. Among them, clustered regularly interspaced short palindromic repeats (CRISPR) loci together with cas (CRISPR-associated) genes form the CRISPR/Cas immune system, which involves partially palindromic repeats separated by short stretches of DNA called spacers, acquired from extrachromosomal elements. It was recently demonstrated that these variable loci can incorporate spacers from infecting bacteriophages and then provide immunity against subsequent bacteriophage infections in a sequence-specific manner. Here we show that the Streptococcus thermophilus CRISPR1/Cas system can also naturally acquire spacers from a self-replicating plasmid containing an antibiotic-resistance gene, leading to plasmid loss. Acquired spacers that match antibiotic-resistance genes provide a novel means to naturally select bacteria that cannot uptake and disseminate such genes. We also provide in vivo evidence that the CRISPR1/Cas system specifically cleaves plasmid and bacteriophage double-stranded DNA within the proto-spacer, at specific sites. Our data show that the CRISPR/Cas immune system is remarkably adapted to cleave invading DNA rapidly and has the potential for exploitation to generate safer microbial strains.     

Continental-scale patterns of canopy tree composition and function across Amazonia

The world's greatest terrestrial stores of biodiversity and carbon are found in the forests of northern South America, where large-scale biogeographic patterns and processes have recently begun to be described. Seven of the nine countries with territory in the Amazon basin and the Guiana shield have carried out large-scale forest inventories, but such massive data sets have been little exploited by tropical plant ecologists. Although forest inventories often lack the species-level identifications favoured by tropical plant ecologists, their consistency of measurement and vast spatial coverage make them ideally suited for numerical analyses at large scales, and a valuable resource to describe the still poorly understood spatial variation of biomass, diversity, community composition and forest functioning across the South American tropics. Here we show, by using the seven forest inventories complemented with trait and inventory data collected elsewhere, two dominant gradients in tree composition and function across the Amazon, one paralleling a major gradient in soil fertility and the other paralleling a gradient in dry season length. The data set also indicates that the dominance of Fabaceae in the Guiana shield is not necessarily the result of root adaptations to poor soils (nodulation or ectomycorrhizal associations) but perhaps also the result of their remarkably high seed mass there as a potential adaptation to low rates of disturbance.     

Biodiversity: disease threat to European fish

The deliberate introduction of new species can have unexpected negative consequences and we show here how a recently introduced fish, the invasive Asian cyprinid Pseudorasbora parva, is causing increased mortality and totally inhibiting spawning in an already endangered native fish, the European cyprinid Leucaspius delineatus. This threat is caused by an infectious pathogen, a rosette-like intracellular eukaryotic parasite that is a deadly, non-specific agent. It is probably carried by healthy Asian fish, and could decrease fish biodiversity in Europe, as well as having implications for commercial aquaculture.     

Photoperiodic induction of synchronous flowering near the Equator

In tropical rainforests, 30-65% of tree species grow at densities of less than one individual per hectare. At these low population densities, successful cross-pollination relies on synchronous flowering. In rainforests with low climatic seasonality, photoperiodic control is the only reliable mechanism for inducing synchronous flowering. This poses a problem because there is no variation in day length at the Equator. Here we propose a new mechanism of photoperiodic timekeeping based on the perception of variation in sunrise or sunset time, which explains and predicts the annually repeated, staggered, synchronous and bimodal flowering of many tree species in Amazonian rainforests near the Equator.     

DNA、字与模型：异常字统计学

大约在15年的时间里，生物学经历了巨大的变化。而这些变化中最重要的变化是DNA序列。计算生物学中一个重要的问题是鉴别短的DNA序列（它在数学上称为字），而这些短序列都具有生物学功能。一种鉴别方法就是决定一个特定的字是否纯粹是随机的，还是由于它出现的频率或所在的位置而具有统计学意义的。     

Identification of presynaptic serotonin autoreceptors using a new ligand: 3H-PAT

Binding studies with appropriate labelled ligands have revealed the existence of two types of serotonin (5-HT) receptor, 5-HT1 and 5-HT2, in the central nervous system of mammals. The 5-HT1 type is characterized by a higher affinity for agonists than for antagonists, whereas the 5-HT2 type binds preferentially to antagonists. However, neither of these receptor types apparently corresponds to the presynaptic autoreceptor controlling 5-HT release. In an attempt to identify the presynaptic autoreceptor directly, we synthesized the tritiated derivative of 8-hydroxy-2-(di-n-propylamino) tetralin (PAT), a new tetralin derivative with potent 5-HT agonist properties and carried out binding studies with rat brain membranes. As we report here, in the hippocampus, the properties of 3H-PAT binding sites correspond closely to those of 5-HT1 sites. In contrast, in the striatum, 3H-PAT binding sites exhibit a subcellular distribution and pharmacological characteristics usually associated with presynaptic autoreceptors. Furthermore, a marked loss of 3H-PAT binding sites occurs in the striatum (but not in the hippocampus) after the selective degeneration of serotoninergic fibres in 5,7-hydroxytryptamine (5,7-HT)-treated rats. Conversely, the sprouting of additional 5-HT terminals in the brain stem of adult rats treated at birth with 5,7-HT is associated with an increased density of 3H-PAT binding sites in this region. 3H-PAT thus seems to be a useful ligand for studying the biochemical and pharmacological characteristics of presynaptic autoreceptors in selected regions of rat brain.