Difficulty overcoming learned non-reward during reversal learning in rats with ibotenic acid lesions of orbital prefrontal cortex.

Behavioral flexibility is a concept often invoked when describing the function of the prefrontal cortex. However, the psychological substrate of behavioral flexibility is complex. Its key components are allocation of attention, goal-directedness, planning, working memory, and response selection.

Mental maps in chacma baboons (Papio ursinus): using inter-group encounters as a natural experiment.

Encounters between groups of wild chacma baboons (Papio ursinus) can be viewed as a natural experiment to investigate the nature of these primates' mental representations of large-scale space. During a 16-month field study in a high population density habitat we recorded the foraging routes and the most important resources of a group of 25 individuals. Also, we estimated the locations of additional baboon groups relative to the study group.

Wza the translocon for E. coli capsular polysaccharides defines a new class of membrane protein.

Many types of bacteria produce extracellular polysaccharides (EPSs). Some are secreted polymers and show only limited association with the cell surface, whereas others are firmly attached to the cell surface and form a discrete structural layer, the capsule, which envelopes the cell and allows the bacteria to evade or counteract the host immune system. EPSs have critical roles in bacterial colonization of surfaces, such as epithelia and medical implants; in addition some EPSs have important industrial and biomedical applications in their own right.

Crystallization of Ranasmurfin, a blue-coloured protein from Polypedates leucomystax.

Ranasmurfin, a previously uncharacterized approximately 13 kDa blue protein found in the nests of the frog Polypedates leucomystax, has been purified and crystallized. The crystals are an intense blue colour and diffract to 1.51 A with P2(1) symmetry and unit-cell parameters a = 40.

Structure of the heterotrimeric PCNA from Sulfolobus solfataricus.

PCNA is a ring-shaped protein that encircles DNA, providing a platform for the association of a wide variety of DNA-processing enzymes that utilize the PCNA sliding clamp to maintain proximity to their DNA substrates. PCNA is a homotrimer in eukaryotes, but a heterotrimer in crenarchaea such as Sulfolobus solfataricus. The three proteins are SsoPCNA1 (249 residues), SsoPCNA2 (245 residues) and SsoPCNA3 (259 residues).

Intrinsic reproductive isolation between Trinidadian populations of the guppy, Poecilia reticulata.

Although Trinidadian populations of the guppy, Poecilia reticulata, show considerable adaptive genetic differentiation, they have been assumed to show little or no reproductive isolation. We tested this assumption by crossing Caroni (Tacarigua River) and Oropuche (Oropuche R.) drainage populations from Trinidad's Northern Range, and by examining multiple aspects of reproductive compatibility in the F1, F2 and BC1 generations.

Mechanism of the Class I KDPG aldolase.

In vivo, 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase catalyzes the reversible, stereospecific retro-aldol cleavage of KDPG to pyruvate and D-glyceraldehyde-3-phosphate. The enzyme is a lysine-dependent (Class I) aldolase that functions through the intermediacy of a Schiff base. Here, we propose a mechanism for this enzyme based on crystallographic studies of wild-type and mutant aldolases.

Structure and function of both domains of ArnA, a dual function decarboxylase and a formyltransferase, involved in 4-amino-4-deoxy-L-arabinose biosynthesis.

Modification of the lipid A moiety of lipopolysaccharide by the addition of the sugar 4-amino-4-deoxy-L-arabinose (L-Ara4N) is a strategy adopted by pathogenic Gram-negative bacteria to evade cationic antimicrobial peptides produced by the innate immune system. L-Ara4N biosynthesis is therefore a potential anti-infective target, because inhibiting its synthesis would render certain pathogens more sensitive to the immune system. The bifunctional enzyme ArnA, which is required for L-Ara4N biosynthesis, catalyzes the NAD(+)-dependent oxidative decarboxylation of UDP-glucuronic acid to generate a UDP-4'-keto-pentose sugar and also catalyzes transfer of a formyl group from N-10-formyltetrahydrofolate to the 4'-amine of UDP-L-Ara4N.

Testing the status-dependent ESS model: population variation in fighter expression in the mite Sancassania berlesei.

The conditional evolutionarily stable strategy (ESS) with status-dependent tactics is the most commonly invoked ESS for alternative reproductive tactics within the sexes. Support for this model has recently been criticized as apparent rather than real. We address key predictions of the status-dependent ESS in three populations of the male dimorphic mite Sancassania berlesei.

Crystal structure and mechanism of a bacterial fluorinating enzyme.

Fluorine is the thirteenth most abundant element in the earth's crust, but fluoride concentrations in surface water are low and fluorinated metabolites are extremely rare. The fluoride ion is a potent nucleophile in its desolvated state, but is tightly hydrated in water and effectively inert. Low availability and a lack of chemical reactivity have largely excluded fluoride from biochemistry: in particular, fluorine's high redox potential precludes the haloperoxidase-type mechanism used in the metabolic incorporation of chloride and bromide ions.

Adenovirus DNA replication.

Replication of the adenovirus genome is catalysed by adenovirus DNA polymerase in which the adenovirus preterminal protein acts as a protein primer. DNA polymerase and preterminal protein form a heterodimer which, in the presence of the cellular transcription factors NFI/CTFI and NFIII/Oct-1, binds to the origin of DNA replication. DNA replication is initiated by DNA polymerase mediated transfer of dCMP onto preterminal protein.

Dispatch. Animal communication: what makes a dog able to understand its master?

The dog has a special relationship with humans, going beyond that of other domestic animals. Recent evidence suggests this comes from domestication rather than wolf behaviour, perhaps involving something as simple as a change in natural looking behaviour.

Structure, conformation, and mechanism in the membrane transport of alkali metal ions by ionophoric antibiotics.

Recent progress in studies of the mechanism of transport of alkali metal ions by ionophoric antibiotics and the structures of alkali metal salts of the ionophores monensin and narasin is reviewed. The structures obtained from 2D NMR experiments in solution provide considerable insights into the mechanisms of transport.

Solid-state transformations of zinc 1,4-benzenedicarboxylates mediated by hydrogen-bond-forming molecules.

The zinc 1,4-benzenedicarboxylates [Zn3(bdc)3(H2O)3] . 4 DMF (1; bdc = 1,4-benzenedicarboxylate), [Zn(bdc)(H2O)] . DMF (2), and [Zn(bdc)] DMF (3) crystallise at room temperature from mixtures of toluene/ dimethylformamide (DMF) under concentrated, dilute and dry conditions, respectively.

Helical Figure-of-Eight Loop Dicopper(I) Compounds: Syntheses, Structures, and Dynamics.

The synthesis of a series of nine large macrocyclic ligands with two N(2)S(2) (thioether and Schiff-base imine) binding sites each, with different bridges between the donor atoms of each site (ethylene, o-xylylene, propylene, butylene) and different spacer groups between the two binding sites (p-xylylene, 2,5-dimethyl-p-xylylene, 2,5-dimethoxy-p-xylylene), and the synthesis of a similar ligand with a preorganized double-helical geometry, based on a paracyclophane spacer group, are reported, together with the syntheses and characterizations of the corresponding dicopper(I) compounds. The solid state structures of the dicopper(I) complexes have two tetrahedral copper(I) sites, separated by ca. 8 Å, and a figure-of-eight loop configuration of the ligand with a parallel arrangement of the two substituted benzene spacer groups (benzene.

Translating the message.

The "one gene = one protein" model for understanding the genome is well-known. But, as with most biological "rules", it has its exceptions. The viral family that brings polio, the common cold and foot-and-mouth disease translates its entire genome into one long "polyprotein".

Tiny TIM: a small, tetrameric, hyperthermostable triosephosphate isomerase.

Comparative structural studies on proteins derived from organisms with growth optima ranging from 15 to 100 degrees C are beginning to shed light on the mechanisms of protein thermoadaptation. One means of sustaining hyperthermostability is for proteins to exist in higher oligomeric forms than their mesophilic homologues. Triosephosphate isomerase (TIM) is one of the most studied enzymes, whose fold represents one of nature's most common protein architectures.

Identification of conserved residues contributing to the activities of adenovirus DNA polymerase.

Adenovirus codes for a DNA polymerase that is a member of the DNA polymerase alpha family and uses a protein primer for initiation of DNA synthesis. It contains motifs characteristic of a proofreading 3'-5'-exonuclease domain located in the N-terminal region and several polymerase motifs located in the C-terminal region. To determine the role of adenovirus DNA polymerase in DNA replication, 22 site-directed mutations were introduced into the conserved DNA polymerase motifs in the C-terminal region of adenovirus DNA polymerase and the mutant forms were expressed in insect cells using a baculovirus expression system.

Overexpression, purification, crystallization and preliminary structural study of dTDP-6-deoxy-L-lyxo-4-hexulose reductase (RmlD), the fourth enzyme of the dTDP-L-rhamnose synthesis pathway, from Salmonella enterica serovar Typhimurium.

L-Rhamnose is an essential component of the cell wall of many pathogenic bacteria. Its precursor, dTDP-L-rhamnose, is synthesized from alpha-D-glucose-1-phosphate and dTTP via a pathway requiring four distinct enzymes: RmlA, RmlB, RmlC and RmlD. RmlD catalyses the terminal step of this pathway by converting dTDP-6-deoxy-L-lyxo-4-hexulose to dTDP-L-rhamnose.

The 3-methylaspartase reaction probed using 2H- and 15N-isotope effects for three substrates: a flip from a concerted to a carbocationic amino-enzyme elimination mechanism upon changing the C-3 stereochemistry in the substrate from R to S.

The mechanisms of the elimination of ammonia from (2S,3S)-3-methylaspartic acid, (2S)-aspartic acid and (2S,3R)-3-methylaspartic acid, catalysed by the enzyme L-threo-3-methylaspartase ammonia-lyase (EC 4.3.1.

Mechanism of 3-methylaspartase probed using deuterium and solvent isotope effects and active-site directed reagents: identification of an essential cysteine residue.

The mechanism of the L-threo-3-methylaspartate ammonia-lyase (EC 4.3.1.

The Friedel-Crafts adducts of methyl oleate with benzene and toluene.

The Friedel-Crafts adducts of methyl oleate with benzene and toluene have been synthesized. The products are a mixture of monomer, dimer and trimer esters together with adducts containing one, two or three molecules of ester per mol of aromatic compound, depending on the proportions of starting material used. The 1H- and 13C-NMR spectra of the adducts are reported together with their mass spectra.

Friedel-Crafts alkylation of benzene and toluene with olefinic C6 hydrocarbons and esters.

To assist our study of the reaction of toluene and other aromatic compounds with methyl oleate and other olefinic esters, benzene and toluene have been alkylated under Friedel-Crafts conditions with hex-1-ene, hex-3-ene, methyl hex-3-enoate and methyl hex-3-enedioate. The products were isolated and identified by NMR and mass spectrometric procedures.