Hyperbolic Modeling of Starburst Dendrimers

Starburst dendrimers are highly branched oligomers. A rigid dendritic hydrocarbon, C₁₁₃₄H₁₁₄₆, has recently been synthesized. It consists of 94 phenylacetylene units displayed in a self-similar two-dimensional skeleton isomorphous to the three-coordinated Bethe lattice. The three-dimensional representation of phenylacetylene dendrimer shows a globular architecture with large voids and niches in its interior, characteristic of hyperbolic surfaces. This work investigates the geometrical scaling behavior of this starburst dendrimer using the symmetry properties of a Bethe lattice embedded in the hyperbolic plane. The results for C₁₁₃₄H₁₁₄₆ provide its density profile and an upper bound for its macromolecular size. This revised version was published online in June 2006 with corrections to the Cover Date.     

Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA

The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from 0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA replicon to be estimated. Received: 14 May 1996 / Accepted: 17 July 1996     

Isoenzymatic characterization of potentially useful forage shrubs belonging to the genus Cytisus and allies (Genistea: Leguminosae)

Twenty-five accessions belonging to the genus Cytisus and allies (Genisteae: Leguminosae), potentially useful for agrosylvopastoral systems in the Mediterranean basin, were analyzed using isoenzymes. The aim was to assess the taxonomic usefulness of these characters at the specific and generic levels, and its value as an aid for the taxonomy. A high level of infrageneric and infraspecific variability was detected. Numerical analysis showed that isoenzymes are useful for the characterization both at the specific and generic levels. The obtained dendrogram supports the generic arrangement proposed by Bisby [(1981) Advances in Legume Systematics, Vol. 1, pp. 409–425], therefore helping to elucidate the difficult taxonomy of the studied species.     

Plasmid rolling circle replication and its control

Abstract This review summarises current information on rolling circle replicating plasmids originally isolated from Gram-positive bacteria with a low guanine and cytosine content in their DNA. It focuses on the peculiar biological features of these small, high copy number plasmids that replicate via an asymmetric RC mechanism. The regulation of plasmid copy number is also discussed.     

Direct effect of the luteinizing hormone releasing hormone analog D-Trp6-Pro9-Net-LHRH on rat testicular steroidogenesis

The luteinizing hormone releasing hormone analog D-Trp⁶-Pro⁹-Net-LHRH (LHRH_a) inhibits rat testicular testosterone secretion. To determine whether LHRH_a decreases serum testosterone concentrations solely by inhibiting gonadotropin secretion or, in addition, by influencing directly testicular testosterone biosynthesis, we examined the effects of LHRH_a on the activities of 5 key testicular steroidogenic enzymes. Thirty hypophysectomized, hCG treated rats were given either LHRH_a (1 μg sc/day) or saline during 7 days. The LHRH_a treated animals exhibited a significant decrease of serum testosterone when compared to the control group (498 ± 37 ng/dl vs 2044 ± 105 ng/dl, mean ± SEM, P 〈0.001). 17-Hydroxyprogesterone serum levels were also decreased in the LHRH_a treated rats (61 ± 6 ng/dl vs 93 ± 7 ng/dl, P 〈0.005), while serum progesterone levels were similar in both groups of animals. These changes in steroid concentrations were associated with decreases in the musomal enzyme activities of 17-hydroxylase (37 ± 9 vs 654 ± 41 pmol/mg protein/min, P 〈0.001), 17, 20-desmolase (103 ± 9 vs 522 ± 47 pmol/mg protein/min, P 〈0.001), 3β-hydroxysteroid dehydrogenase (1.7 ± 0.02 vs 4.1 ± 0.1 nmol/mg protein/min, P 〈0.001), aromatase (95 ± 7 vs 228 ± 6 pmol/mg protein/ min, P 〈0.001) and 17-ketosteroid reductase (167 ± 9 vs 290 ± 18 pmol/mg protein/min, P 〈0.01) in the LHRH_a treated animals. These findings indicate that LHRH_a can inhibit directly rat testicular testosterone biosynthesis.     

β-Alanine transport into plasma membrane vesicles derived from rat brain synaptosomes

Transport of -alanine has been demonstrated in membrane vesicles isolated from rat brain, using artificially imposed ion gradients as the sole energy source. The uptake of -alanine is strictly dependent on the presence of Na⁺ and Cl^– in the medium, and the process can be driven either by an Na⁺ gradient (out > in) or by a Cl^– gradient (out > in) when the other essential ion is present. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of ionophore valinomycin and anions with different permeabilities. -Alanine uptake is inhibited by the presence of GABA.     

Changes in protein synthesis in rats in response to endurance training

Experiments were conducted to investigate the influence of endurance exercise training on protein synthesis in skeletal muscle, heart, and liver. Training decreased incorporation of [¹⁴C]-leucine into proteins of the stromal fraction of muscle but there was no change in amino acid incorporation into proteins of the sarcoplasmic and myofibrillar fractions. Incorporation of [¹⁴C]-leucine into the protein of heart, liver, and plasma was depressed in trained rats compared to untrained rats. The specific radioactivity of [¹⁴C]-leucine was similar in tissues of trained and untrained rats and thus the depressed amino acid incorporation represents a decrease in the rate of protein synthesis. These observations demonstrate that the adaptation of muscle protein metabolism to endurance training is quite different than the alterations during work-induced hypertrophy of muscle. The difference in adaptation probably relates to the functional differences between the types of exercise. However depression of protein synthesis in trained rats is a general effect in several tissues and not an effect localized in muscle tissue.     

The Cladocera of Sri Lanka (Ceylon), with remarks on some species

The freshwater Cladocera of Sri Lanka has been revised based on the study of over 700 zooplankton samples collected from all habitat types during 1965–1980. The cladoceran fauna is represented by six families; members of the families Polyphemidae, Leptodoridae and Holopedidae are absent. The common temperate genus Daphnia is rare.Sixty-two species have been recorded from Sri Lanka. Of these, five are new records. Remarks on a few species are given with illustrations. The distribution of Cladocera in different types of habitats is discussed. The greatest species diversity was found in ponds. The Sri Lankan fauna is numerically and in species diversity typical of tropical cladoceran fauna. It resembles the southern Indian fauna very closely except for the absence in Sri Lanka of the genera Acroperus and Camptocercus.     

Spore survival during batch dry rendering of abattoir waste.

Normal batch dry rendering practice does not ensure sterile products, because bacterial spores are protected against thermal denaturation by the high fat-low water content environment which results from drying the materials at temperatures below those required for sterilization.