The membrane topology of the Rhizobium meliloti C4-dicarboxylate permease (DctA) as derived from protein fusions with Escherichia coli K12 alkaline phosphatase (PhoA) and β-galactosidase (LacZ)

The Rhizobium meliloti dctA gene encodes the C₄-dicarboxylate permease which mediates uptake of C₄-dicarboxylates, both in free-living and symbiotic cells. Based on the hydrophobicity of the DctA protein, 12 putative membrane spanning regions were predicted. The membrane topology was further analysed by isolating in vivo fusions of DctA to Escherichia coli alkaline phosphatase (PhoA) and E. coli β-galactosidase (LacZ). Of 10 different fusions 7 indicated a periplasmic and 3 a cytoplasmic location of the corresponding region of the DctA protein. From these data a two-dimensional model of DctA was constructed which comprised twelve transmembrane α-helices with the amino-terminus and the carboxy-terminus located in the cytoplasm. In addition, four conserved amino acid motifs present in many eukaryotic and prokaryotic transport proteins were observed.     

MINIMAL MALE/FEMALE TRADEOFFS IN ZIZANIA PALUSTRIS,A MONOECIOUS ANNUAL GRASS

Because a male/female resource tradeoff is a basic assumption of many models of sex allocation in cosexual plants, statistical and manipulative methods were used to look for evidence of intersexual resource conflicts in Zizania palustris. In this monoecious grass, male and female investments overlap in time within each panicle and on successive panicles, and sex allocation quickly responds to environmental changes. Nevertheless, no negative correlations were found between the numbers of florets of each sex within panicles, on consecutive panicles, or on whole plants. Removing immature fruits or florets of either sex did not significantly increase subsequent investment in the other sex. The one significant tradeoff was slightly lower total fruit production on plants with exceptionally large male investment. Wild rice, therefore, fits the tradeoff assumption of sex allocation models at the population level but rarely at the individual level.     

Late Famennian gastropoda from south-west England

The gastropod fauna of the Upper Devonian Baggy and Pilton formations in south‐west England is revised and includes some 30 taxa. The topmost part of the Upper Famennian succession in Devon is represented by clastic near‐shore and shallow shelf sediments, indicating a short‐term transgressive phase (‘Strunian Transgression’). The sequence yields a highly diverse fauna dominated by brachiopods and ostracodes, locally supplemented by crinoids, bryozoans, trilobites and molluscs. The taxa ‘Patellostium’britannicum sp. nov., Angyomphalus (Angyomphalus) junius sp. nov. and Dictyotomaria eurocapillaria sp. nov. are erected; a junior homonym is replaced by Macrochilina? piltonensis nom. nov. The gastropod fauna displays an independent character, where latest Devonian faunal elements overlap with Late Palaeozoic taxa expressing a transition similar to that of the bivalves, brachiopods, echinoderms and corals, without a sharp faunal break at the Devonian/Carboniferous boundary. Apart from the Caenogastropoda, all subclasses of gastropods are represented. Members of the bellerophontoids, pleurotomarioids and loxonematoids are most abundant, followed by murchisonioids, naticimorphs, euomphalomorphs and platyceratoids. The various gastropod groups represent different ecological demands and trophic categories, and together with the accompanying fauna indicate that nearly all habitats and niches were occupied in the shallow South Laurussian Shelf.     

Territorial Pheromones of Female Red-backed Salamanders

Pheromones provide an important source of communication during social interactions of caudate amphibians. To further examine their use in territorial defense, we performed a laboratory experiment to test the hypothesis that non-courting female red-backed salamanders (Plethodon cinereus) deposit pheromones in or on fecal pellets, as males are known to do during territorial advertisement. Four conditions were tested: (1) a burrow marked with a female's own pellet vs. a burrow marked by a conspecific female's pellet, (2) own vs. unmarked burrows, (3) conspecific vs. unmarked burrows, and (4) paired unmarked burrows as a control. Females nose-tapped (for olfactory cues) their own and conspecific pellets about equally. However, they spent significantly more time in both threat and submissive behavior toward the conspecific pellets and spent significantly more time in their own marked burrows. We infer that female P. cinereus do deposit pheromones in or on fecal pellets and that these pellets may be used to advertise territories. The behavioral responses of females toward pellets of other females were more aggressive than those of males (in a previous study) toward pellets of other males.     

Evolutionary Relationship of the Ligand-Gated Ion Channels and the Avermectin-Sensitive,Glutamate-Gated Chloride Channels

Two cDNAs, GluClα and GluClβ, encoding glutamate-gated chloride channel subunits that represent targets of the avermectin class of antiparasitic compounds, have recently been cloned from Caenorhabditis elegans (Cully et al., Nature, 371, 707–711, 1994). Expression studies in Xenopus oocytes showed that GluClα and GluClβ have pharmacological profiles distinct from the glutamate-gated cation channels as well as the γ-aminobutyric acid (GABA)- and glycine-gated chloride channels. Establishing the evolutionary relationship of related proteins can clarify properties and lead to predictions about their structure and function. We have cloned and determined the nucleotide sequence of the GluClα and GluClβ genes. In an attempt to understand the evolutionary relationship of these channels with the members of the ligand-gated ion channel superfamily, we have performed gene structure comparisons and phylogenetic analyses of their nucleotide and predicted amino acid sequences. Gene structure comparisons reveal the presence of several intron positions that are not found in the ligand-gated ion channel superfamily, outlining their distinct evolutionary position. Phylogenetic analyses indicate that GluClα and GluClβ form a monophyletic subbranch in the ligand-gated ion channel superfamily and are related to vertebrate glycine channels/receptors. Glutamate-gated chloride channels, with electrophysiological properties similar to GluClα and GluClβ, have been described in insects and crustaceans, suggesting that the glutamate-gated chloride channel family may be conserved in other invertebrate species. The gene structure and phylogenetic analyses in combination with the distinct pharmacological properties demonstrate that GluClα and GluClβ belong to a discrete ligand-gated ion channel family that may represent genes orthologous to the vertebrate glycine channels. Received: 30 September 1996 / Accepted: 15 November 1996     

Human DNA helicase IV is nucleolin, an RNA helicase modulated by phosphorylation

The cDNA encoding human DNA helicase IV (HDH IV), a 100-kDa protein which unwinds DNA in the 5′ to 3′ direction with respect to the bound strand, was cloned and sequenced. It was found to be identical to the human cDNA encoding nucleolin, a ubiquitous eukaryotic protein essential for pre-ribosome assembly. HDH IV/nucleolin can unwind RNA-RNA duplexes, as well as DNA-DNA and DNA-RNA duplexes. Phosphorylation of HDH IV/nucleolin by cdc2 kinase and casein kinase II enhanced its unwinding activity in an additive way. The Gly-rich C-terminal domain possesses a limited ATP-dependent duplex-unwinding activity which contributes to the helicase activity of HDH IV/nucleolin.     

Interaction of influenza virus proteins with planar bilayer lipid membranes II. Effects of rimantadine and amantadine

The dependence of the surface potential difference (ΔU), transversal elasticity module (E₁) and membrane conductivity (G₀) on the concentrations of the antiviral drugs, rimantadine and amantadine was studied in the planar bilayer lipid membrane system. The method used was based on independent measurements of the second and third harmonics of the membrane capacitance current. The binding constants of bilayer lipid membranes obtained from the drug adsorption isotherms were 2.1 · 10⁵ M^?1 and 1.3 · 10⁴ M^?1 for rimantadine and amantadine, respectively. The changes in G₀ took place only after drug adsorption saturation had been achieved. The influence of rimantadine and amantadine on the interaction of bilayer lipid membranes with matrix protein from influenza virus was also investigated. The presence of 70 μg/ml rimantadine in the bathing solution resulted in an increase in the concentration of M-protein at which the adsorption and conductance changes were observed. The effects of amantadine were similar to those of rimantadine but required a higher critical concentration of amantadine. The results obtained suggest that the antiviral properties of rimantadine and amantadine may be related to the interaction of these drugs with the cell membrane, which can affect virus penetration into the cell as well as maturation of the viral particle at the cell membrane.     

Cell wall-lytic activity in Chlorella fusca

The soluble fraction of homogenates of synchronous Chlorella fusca was tested for carbohydrate-lyzing activities. With isolated cell walls and -1,4-mannan or carboxymethyl cellulose as substrates, a sharp increase in activity occurred shortly before release of the daughter cells followed by a decline during release. The lytic activities were partially purified by ammonium sulphate precipitation and analyzed by gel filtration on a calibrated column. Apparent molecular weights were 27,000 for cell wall autolysin(s) and -1,4-mannanase, 36,000 for carboxymethyl cellulase and 70,000 for another -1,4-mannanase. Incubation of isolated cell walls with an enzyme preparation purified by ammonium sulphate precipitation resulted in release of up to 70% of the cell wall carbohydrate as monosaccharide, predominantly mannose and glucose. The carbohydrate released in vivo into the culture medium shortly before and during liberation of the daughter cells consisted largely of polymeric material with rhamnose, fucose and mannose as main constitutents. Upon poisoning the cells with NaN₃ or carbonyl cyanide p-trifluoromethoxy-phenylhydrazone, however, a monosaccharide fraction consisting of mannose and glucose was predominant in the medium. It is suggested that the major products of cell wall lysis in vivo are monosaccharides which are rapidly taken up and metabolized by the developing daughter cells in an energy-dependent manner.     

α-Thalassemia among sickle cell anemia patients in various African populations

Summary We have studied the incidence of -thalassemia in normal and SS individuals from Senegal, Benin, Upper Volta, and Central Republican Africa. The thal gene frequency is not significantly different in the controls from the various populations and in the SS patients from Senegal. In contrast it is compatible with increased survival of SS patients in Benin, Upper Volta. The data suggest epistatic effects of other factors in the Senegalese population.     

Isoelectric focusing of glutathione S-transferases from rat liver and kidney

The glutathione S-transferases that were purified to homogeneity from liver cytosol have overlapping but distinct substrate specificities and different isoelectric points. This report explores the possibility of using preparative electrofocusing to compare the composition of the transferases in liver and kidney cytosol. Hepatic cytosol from adult male Sprague–Dawley rats was resolved by isoelectric focusing on Sephadex columns into five peaks of transferase activity, each with characteristic substrate specificity. The first four peaks of transferase activity (in order of decreasing basicity) are identified as transferases AA, B, A and C respectively, on the basis of substrate specificity, but the fifth peak (pI6.6) does not correspond to a previously described transferase. Isoelectric focusing of renal cytosol resolves only three major peaks of transferase activity, each with narrow substrate specificity. In the kidney, peak 1 (pI9.0) has most of the activity toward 1-chloro-2,4-dinitrobenzene, peak 2 (pI8.5) toward p-nitrobenzyl chloride, and peak 3 (pI7.0) toward trans-4-phenylbut-3-en-2-one. Renal transferase peak 1 (pI9.0) appears to correspond to transferase B on the basis of pI, substrate specificity and antigenicity. Kidney transferase peaks 2 (pI8.5) and 3 (pI7.0) do not correspond to previously described glutathione S-transferases, although kidney transferase peak 3 is similar to the transferase peak 5 from focused hepatic cytosol. Transferases A and C were not found in kidney cytosol, and transferase AA was detected in only one out of six replicates. Thus it is important to recognize the contribution of individual transferases to total transferase activity in that each transferase may be regulated independently.