Effects of lateral amygdala lesions on the responses to novelty in mice

Bilateral electrolytic lesions restricted to the lateral, basolateral and basomedial amygdaloid nuclei in mice produced a lack of avoidance responses towards novel stimuli. While controls showed avoidance and burying reactions to a novel object introduced into their familiar environment, lesioned mice displayed a high number of approach responses and a low level of burying reactions. Furthermore, when given the opportunity to move around freely in simultaneously presented novel and familiar places, control mice at first exhibited avoidance reactions to the novel environment before showing novelty preference. There were no avoidance reactions in lesioned mice. These data are consistent with the hypothesis that amygdala plays a specific role in the regulation of defensive reactions.     

Co-fermentation of xylose and cellobiose by an engineered Saccharomyces cerevisiae

We have integrated and coordinately expressed in Saccharomyces cerevisiae a xylose isomerase and cellobiose phosphorylase from Ruminococcus flavefaciens that enables fermentation of glucose, xylose, and cellobiose under completely anaerobic conditions. The native xylose isomerase was active in cell-free extracts from yeast transformants containing a single integrated copy of the gene. We improved the activity of the enzyme and its affinity for xylose by modifications to the 5′-end of the gene, site-directed mutagenesis, and codon optimization. The improved enzyme, designated RfCO*, demonstrated a 4.8-fold increase in activity compared to the native xylose isomerase, with a K_m for xylose of 66.7?mM and a specific activity of 1.41?μmol/min/mg. In comparison, the native xylose isomerase was found to have a K_m for xylose of 117.1?mM and a specific activity of 0.29?μmol/min/mg. The coordinate over-expression of RfCO* along with cellobiose phosphorylase, cellobiose transporters, the endogenous genes GAL2 and XKS1, and disruption of the native PHO13 and GRE3 genes allowed the fermentation of glucose, xylose, and cellobiose under completely anaerobic conditions. Interestingly, this strain was unable to utilize xylose or cellobiose as a sole carbon source for growth under anaerobic conditions, thus minimizing yield loss to biomass formation and maximizing ethanol yield during their fermentation.     

Characterization of a light-dependent glutamate synthase activity in Chlamydomonas reinhardtii

Photosynthetically active vesicles prepared from Chlamydomonas reinhardtii retained a light-dependent glutamate synthase activity which was highly specific for 2-oxoglutarate (K_m=2.1 mM) and L-glutamine (K_m=0.9 mM) as amido group acceptor and donor respectively. This activity was inhibited by azaserine, p-hydroxymercuribenzoate and 3-(p-chlorophenyl)-1,1-dimethyl urea.Light-dependent synthesis of glutamate was also obtained by coupling Chlamydomonas photosynthetic particles to purified ferredoxin-glutamate synthase, using ascorbate and 2,6-dichlorophenol-indophenol as electron donor. This system was also specific for 2-oxoglutarate (K_m=1 mM) and L-glutamine (K_m=0.8 mM) as substrates, and was stimulated by dithioerythritol. Azaserine and p-hydroxymercuribenzoate, but not 3-(p-chlorophenyl)-1,1-dimethyl urea, inhibited the reconstituted activity; high concentrations of 2-oxoglutarate were inhibitory.Abbreviations A Absorbance - CCP p-Trichlorometoxi-carbonylcyanide-phenylhydrazone - Chl Chlorophyll - CMU 3-(p-Chlorophenyl)-1,1-dimethyl urea - DPIP 2,6-Dichlorophenol-indophenol - DTE Dithioerythritol - MSX L-Methionine, D-L, sulfoximine - MV Methyl viologen     

Selective emergence and survival of early polypeptides in water

Oligopeptides essential to primitive cells could not be obtained just by raising the background noise of organic compounds produced by a prebiotic chemistry working at random. Selection pathways were required. Experimental evidence is given for selective condensation of amino acids in water as well as for selective resistance to degradation. It is shown that N-carboxyanhydrides are good candidates for chemical selection in water. They are formed when active esters of amino acids are left in the presence of bicarbonate ions or when N,N'-carbonyldiimidazole is used as condensing agent. Polymerization of a mixture of proteinaceous and non-proteinaceous amino acids leads to an enrichment in the proteinaceous ones plusα-aminobutyric acid. Selective resistance toward degradation ofβ-pleated sheet conformation is used to exemplify a possible accumulation of homochiral sequences made of hydrophilic and strong hydrophobic residues. Amino acids with branched aliphatic side-chains are selected but those having short linear aliphatic side-chains such asα-aminobutyric acid or norvaline are not.     

Cell wall strength of Hansenula polymorpha in continuous cultures in relation to the recovery of methanol oxidase (MOX)

Summary The changes in cell wall strength of Hansenula polymorpha have been investigated in continuous cultures with respect to the recovery of methanol oxidase (MOX). Cultures grown on several substrate mixtures that enable induction of MOX have been compared with cultures grown on methanol as the sole inducer. The effects of dilution rate (D) on lysis properties have been studied. The cell wall strength was consistently influenced by growth media and D. Media containing glycerol/methanol showed the slowest lysis kinetics, with a large fraction of non-degradable cell wall material. In continuous cultures grown on a mixture of glucose and methanol both the resistance to zymolyase and the mean cell wall thickness increased at D<0.1 h^–1. The yield of MOX by zymolyase lysis is reproducible and up to 100% higher than that of the standard ultrasonic treatment. The lysis kinetics indicated that zymolyase punctures the cell wall; since the release rate of MOX is lower than that of protein, the cell contents will leak through. At D-values>0.2 h^–1, both protein and MOX release rates increase, reflecting a change in lysis mechanism due to the increased fraction of thin daughter cells. Kinetic analysis of zymolyase lysis using both physical and enzymatic methods provides information for achieving optimal recovery of MOX.Abbreviations and symbols C _MOX MOX activity [MOX units·g X^–1] - D dilution rate [h^–1] - MOX methanol oxidase - k_c decay rate constant of A 610 nm [min^–1] - k_d decay constant of MOX activity [min^–1] - k_dis dissociation rate constant [min^–1] - k_MOX release rate constant of MOX activity [min^–1] - k_p release rate constant of protein [min^–1] - R recovery efficiency of enzyme [-] - St stability of enzyme [-]     

Presence of nucleosomes inPenicillium chrysogenum

We have studied the chromatin structure ofPenicillium chrysogenum. This fungus presents the typical nucleosomal repeat and the core DNA size characteristic of all the eukaryotes. The repeat length (about 180 base pairs) is in the range of those obtained for most fungi (160–180 base pairs) and shorter than in higher eukaryotes. Knowledge aboutP. chrysogenum chromatin structure opens the way to the study of the mechanisms of genetic regulation in this filamentous fungus.     

Fragile sites,chromosome evolution,and human neoplasia

Summary In a study of the possible relationship between human fragile sites, chromosomal rearrangements related to neoplasia, and chromosome regions involved in evolutionary changes, we have found that 17 fragile sites related to cancer, 15 fragile sites not related to cancer, and 17 non-fragile regions also related to human malignancy correspond or are close to bands involved in rearrangements that have taken place during chromosomal evolution in primates.     

Effect of HCO - 3 concentration in the absorption solution on the energetic coupling of H+-cotransports in roots of Zea mays L.

The effect of HCO ₃ ^- on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO₂ partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H⁺ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO ₃ ^- accumulation were slowed down, while ⁸⁶Rb⁺ uptake and K⁺ accumulation rates were increased by HCO ₃ ^- . These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H⁺ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO₂/H₂CO₃/HCO ₃ ^- accelerated the diffusion of equivalent H⁺ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW fresh weight - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - J_aa acetic acid influx - J_K ⁺ K⁺ influx - J_Pi orthophosphate influx - Mes 2-(N-morpholino)ethanesulfonic acid - pCO₂ CO₂ partial pressure - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Continuous production of gibberellic acid in a fixed-bed reactor by immobilized mycelia of Gibberella fujikuroi in calcium alginate beads

Summary The continuous production of gibberellic acid with immobilized mycelia of Gibberella fujikuroi was maintained over a hundred days in a tubular fixed-bed reactor. Free mycelium at the beginning of the storage phase was harvested from G. fujikuroi shake-flask culture and was immobilized by ionotropic gelation in calcium alginate beads.The continuous recycle production system consisted of a fixed-bed reactor, a container in which the culture medium was heated, stirred and aerated, and valves for sample withdrawal or reactant addition during the first 1320 h (55 days). A two-phase continuous extractor was then added for the last 960 hours (40 days). Free and immobilized mycelium shake-flask cultures with the same strain used in the continuous culture system were also realized to compare growth, maintenance and production parameters. The results show about the same gibberellic acid productivity in both free and immobilized mycelium shakeflask cultures: 0.384 and 0.408 mgGA₃·gBiomass^-1 ·day^-1, respectively, whereas in the continuous system the gibberellic acid production is about twice as large for a similar biomass: 0.768 mgGA₃·gBiomass^-1·day^-1. Several factors affecting the overall productivity of the immobilized systems were found to be: the quality and the quantity of mycelia in the biocatalyst beads and the immobilization conditions.     

Subcellular localization of calcium in sporangiophores of Phycomyces blackesleeanus

The in situ localization of Ca²⁺ in stage I sporangiophores of the fungus Phycomyces blakesleeanus was achieved with the potassium pyroantimonate technique. Precipitates of calcium-antimonate were present in mitochondria, vacuoles, endoplasmic reticulum and adjacent cytoplasm, Golgi-like bodies, and nuclei but not cell walls. Material treated with the calcium chelator EGTA lacked these precipitates. The preferential localization of Ca²⁺ in mitochondria, endoplasmic reticulum and vacuoles suggests that these organelles modulate the level of this cation in sporangiophores of P. blakesleeanus.Abbreviations EGTA ethyleneglycol-bis-(-aminoethyl ether) N,N, tetraacetic acid