Nesting Behaviour of Abert Squirrels (Sciurus aberti)

Nesting behaviour of Abert squirrels (Sciurus aberti), including site selection and use, was studied in the foothills of the Rocky Mountains in Boulder County, Colorado. Only females were observed building nests, although both males and females maintained nests once they were built. Communal nesting by Abert squirrels was rare, but the majority of observed nest sharings involved unrelated male and female pairs. A total of 14 variables were used to evaluate the nests (n = 49) inhabited by Abert squirrels from May 1988 to Jun. 1991. All nests were located in Ponderosa pine (Pinus ponderosa) trees. The majority of nests were constructed of twigs and located in the upper one-third of the canopy, near the trunk, on the south-east side of the tree. Trees with nests were predominantly located in closed stands. Nest trees, when compared with unused control trees that were equally accessible to squirrels, were significantly different from control trees in five of nine variables. Nest tree crowns intertwined with a larger number of adjacent tree crowns than did control tree crowns. Nest trees were also significantly taller than control trees, but subdominant to adjacent trees within a stand. Seasonal and diurnal patterns of nest use indicate that Abert squirrels do not choose nest locations on the south-east sides of trees to facilitate behavioural thermoregulation. Rather, Abert squirrels select nest site locations to (1) maximize accessibility and (2) maximize structural stability which may provide protection from wind and rain.     

Structure determination of the disialylated poly-(N-acetyllactosamine)-containingO-linked carbohydrate chains of equine chorionic gonadotropin

The disialylated poly-(N-acetyllactosamine)-containingO-linked oligosaccharide alditols, released by alkaline borohydride treatment of the enzymicallyN-deglycosylated β-subunit of equine chorionic chonadotropin, were purified by fast protein liquid chromatography (FPLC) on Mono Q and analysed by fast ion bombardment mass spectrometry (FAB-MS) and¹H-NMR spectroscopy. The identified oligosaccharide alditols have the following structure: $$\begin{gathered} Neu5Ac\alpha 2 - 3\left[ {Gal\beta 1 - 4GlcNAc\beta 1 - 3} \right]_{0 - 4} Gal\beta 1 - 4GlcNAc\beta 1 - 6 \hfill \\ \begin{array}{*{20}c} { \backslash } \\ { GalNAc - ol} \\ { /} \\ {Neu5Ac\alpha 2 - 3Gal\beta 1 - 3} \\ \end{array} \hfill \\ \end{gathered}$$      

Inheritance of Strain Instability (Sectoring) in the Commercial Button Mushroom, Agaricus bisporus

The button mushroom, Agaricus bisporus, is a commercially important cultivated filamentous fungus. During the last decade, the button mushroom industry has depended mainly on two strains (or derivatives of these two strains). Using one of these highly successful strains (strain U1) we examined the phenomenon of strain instability, specifically, the production of irreversible sectors. Three “stromatal” and three “fluffy” sectors were compared with a healthy type U1 strain and with a wild-collected isolate. Compost colonization and fruit body morphology were examined. The main objective of this study, however, was to examine the meiotic stability of the sectored phenotype. Single basidiospores were isolated and subjected to a grain bioassay in which the ability to produce sectors was measured. Our results were as follows: (i) basidiospore cultures obtained from a wild-collected isolate showed no tendency to produce sectors; (ii) approximately 5% of the basidiospore cultures obtained from healthy type U1 strains produced irreversible sectors in the grain bioassay; (iii) the five primary sectors examined produced basidiospore cultures, half of which produced normal-looking growth in the grain bioassay and half of which produced some degree of sectoring; and (iv) the one sectored isolate that represented the F2 generation gave ratios similar to the 1:1 ratio observed for the F1 cultures.     

Interrelationships of Leucine and Glutamate Metabolism in Cultured Astrocytes

Abstract: The aim was to study the extent to which leu-cine furnishes α-NH₂ groups for glutamate synthesis via branched-chain amino acid aminotransferase. The transfer of N from leucine to glutamate was determined by incubating astrocytes in a medium containing [¹⁵N]leucine and 15 unlabeled amino acids; isotopic abundance was measured with gas chromatography-mass spectrometry. The ratio of labeling in both [¹⁵N]glutamate/[¹⁵N]leucine and [2-¹⁵N]glutamine/[¹⁵N]leucine suggested that at least one-fifth of all glutamate N had been derived from leucine nitrogen. At the same time, enrichment in [¹⁵N]leucine declined, reflecting dilution of the ¹⁶N label by the unlabeled amino acids that were in the medium. Isotopic abundance in [¹⁶N]-isoleucine increased very quickly, suggesting the rapidity of transamination between these amino acids. The appearance of ¹⁵N in valine was more gradual. Measurement of branched-chain amino acid transaminase showed that the reaction from leucine to glutamate was approximately six times more active than from glutamate to leucine (8.72 vs. 1.46 nmol/min/mg of protein). However, when the medium was supplemented with α-ketoisocaproate (1 mM), the ketoacid of leucine, the reaction readily ran in the “reverse” direction and intraastrocytic [glutamate] was reduced by ～50% in only 5 min. Extracellular concentrations of α-ketoisocaproate as low as 0.05 mM significantly lowered intracellular [glutamate]. The relative efficiency of branched-chain amino acid transamination was studied by incubating astrocytes with 15 unlabeled amino acids (0.1 mM each) and [¹⁵N]glutamate. After 45 min, the most highly labeled amino acid was [¹⁵N]alanine, which was closely followed by [¹⁵N]leucine and [¹⁵N]isoleucine. Relatively little ¹⁵N was detected in any other amino acids, except for [¹⁵N]serine. The transamination of leucine was ～17 times greater than the rate of [1-¹⁴C]leucine oxidation. These data indicate that leucine is a major source of glutamate nitrogen. Conversely, reamination of a-ketoisocaproate, the ketoacid of leucine, affords a mechanism for the temporary “buffering” of intracellular glutamate.     

Pigment interactions in chlorosomes of various green bacteria

Resonance Raman experiments were performed on different green bacteria. With blue excitation, i.e. under Soret resonance or preresonance conditions, resonance Raman contributions were essentially arising from the chlorosome pigments. By comparing these spectra and those of isolated chlorosomes, it is possible to evaluate how the latter retain their native structure during the isolation procedures. The structure of bacteriochlorophyll oligomers in chlorosomes was interspecifically compared, in bacteriochlorophyllc- and bacteriochlorophylle- synthesising bacteria. It appears that interactions assumed by the 9-keto carbonyl group are identical inChlorobium limicola, Chlorobium tepidum, andChlorobium phaeobacteroides. In the latter strain, the 3-formyl carbonyl group of bacteriochlorophylle is kept free from intermolecular interactions. By contrast, resonance Raman spectra unambiguously indicate that the structure of bacteriochlorophyll oligomers is slightly different in chlorosomes fromChloroflexus auranticus, either isolated or in the whole bacteria.     

Principles and practices of medicine

The medical textbooks in our university library present ‘principles’ as the basis which underlies medical ‘practice’. In this article it is argued that this helps different medical logics to co-exist. The example analyzed is that of anemia in the Netherlands. Currently this is defined pathophysiologically, statistically and clinically. These three definitions are intertwined with different strategies for the creation of normal hemoglobin levels and the detection of patients with anemia. The discrepancies between them, however, do not lead to the controversies that might be expected by those who believe in consistency. Instead, the rhetoric of principles-and-practice helps to bring about peaceful co-existence.     

Molecular analysis of the aspartate kinase-homoserine dehydrogenase gene from Arabidopsis thaliana

The gene encoding Arabidopsis thaliana aspartate kinase (ATP:L-aspartate 4-phosphotransferase, EC 2.7.2.4) was isolated from genomic DNA libraries using the carrot ak-hsdh gene as the hybridizing probe. Two genomic libraries from different A. thaliana races were screened independently with the ak probe and the hsdh probe. Nucleotide sequences of the A. thaliana overlapping clones were determined and encompassed 2 kb upstream of the coding region and 300 bp downstream. The corresponding cDNA was isolated from a cDNA library made from poly(A)⁺-mRNA extracted from cell suspension cultures. Sequence comparison between the Arabidopsis gene product and an AK-HSDH bifunctional enzyme from carrot and from the Escherichia coli thrA and metL genes shows 80%, 37.5% and 31.4% amino acid sequence identity, respectively. The A. thaliana ak-hsdh gene is proposed to be the plant thrA homologue coding for the AK isozyme feedback inhibited by threonine. The gene is present in A. thaliana in single copy and functional as evidenced by hybridization analyses.The apoprotein-coding region is interrupted by 15 introns ranging from 78 to 134 bp. An upstream chloroplast-targeting sequence with low sequence similarity with the carrot transit peptide was identified. A signal sequence is proposed starting from a functional ATG initiation codon to the first exon of the apoprotein. Two additional introns were identified: one in the 5 non-coding leader sequence and the other in the putative chloroplast targeting sequence. 5 sequence analysis revealed the presence of several possible promoter elements as well as conserved regulatory motifs. Among these, an Opaque2 and a yeast GCN4-like recognition element might be relevant for such a gene coding for an enzyme limiting the carbon-flux entry to the biosynthesis of several essential amino acids. 3 sequence analysis showed the occurrence of two polyadenylation signals upstream of the polyadenylation site.This work is the first report of the molecular cloning of a plant ak-hsdh genomic sequence. It describes a promoter element that may bring new insights to the regulation of the biosynthesis of the aspartate family of amino acids.Abbreviations AK aspartate kinase - HSDH homoserine dehydrogenase - ID intermediate domain - Tp transit peptide