Sequence of the mglB gene from Escherichia coli K12: comparison of wild-type and mutant galactose chemoreceptors

Summary The mglB gene of Escherichia coli codes for a galactose-binding protein (GBP) that serves both as the galactose chemoreceptor and as the recognition component of the -methylgalactoside transport system. The mglB551 mutation eliminates the chemotactic function of GBP without altering its transport or substrate-binding properties. To investigate the interaction between GBP and Trg, the chemotactic signal transducer for galactose, we sequenced the mglB genes from wild-type and mglB551 mutant strains. The mutation causes the replacement of Gly₇₄ of GBP by Asp. This residue is located in alpha-Helix III at the tip of the P domain in the GBP tertiary structure farthest removed from the substrate-binding cleft between the P and Q domains. We conclude that Helix III must be part of, or at least adjacent to, the recognition site for Trg. Our sequence also included part of the mglA gene, which is immediately distal to mglB. The amino acid sequence deduced for the beginning of the MglA protein showed homology with a family of polypeptides that contain an ATP-binding site and are components of binding-protein-dependent transport systems.     

The pattern of proliferation of the neuroblasts in the wild-type embryo of Drosophila melanogaster

Summary The pattern of neuroblast divisions was studied in thoracic and abdominal neuromeres of wild-type Drosophila melanogaster embryos stained with a monoclonal antibody directed against a chromatin-associated antigen. Since fixed material was used, our conclusions are based upon the statistical evaluation of a large number of accurately staged embryos, covering the stages between the formation of the cephalic furrow up to shortened germ band. Our observations point to a rather stereotypic pattern of proliferation, consisting of several parasynchronous cycles of division. The data suggest that all SI neuroblasts divide at least eight times, all SII neuroblasts six or seven times and all SIII neuroblasts at least five times. This conclusion is based on the mapping of mitotic neuroblasts and is supported by the progressive reduction of the neuroblast volume and by the results of cell countings performed on embryos of increasing age. No conclusive evidence was obtained concerning the fate of the neuroblasts after their last mitosis, i.e. it cannot be decided whether the neuroblasts degenerate or become incorporated as inconspicuous cells in the larval ventral cord. The duration of the cycles of division of the neuroblasts was found to be 40–50 min each, while in the case of ganglion mother cells about 100 min are required to complete one cell cycle.     

Induced parasexual processes in Claviceps sp. strain SD58.

A homokaryotic, clavine alkaloid-producing strain of ergot, Claviceps sp. strain SD 58, was used in an attempt to demonstrate parasexuality. Genetically marked auxotrophic strains were produced by mutation with N-methyl-N'-nitro-N-nitrosoguanidine. Protoplast fusion of pairs of unlike doubly auxotrophic strains and isolation of stable prototrophic fusion products were carried out. By growth of the fusion products on complete medium, selective pressure for prototrophy was removed and auxotrophic segregants were allowed to form. Analysis of these and recovery of segregants with nonleaky, non-parent-type combinations of auxotrophic characteristics has provided strong evidence that a parasexual cycle can function in Claviceps sp. strain SD 58. Preliminary work suggests that the genetics of ergot might be studied by mitotic analysis and that protoplast fusion and selection procedures might be useful for the enhancement of favorable characteristics in Claviceps strains.     

Characterization of the Effects of Divalent Cations on the Coupled Activities of the H-ATPase in Tonoplast Vesicles

The substrate requirement of the H⁺-ATPase in purified corn root tonoplast vesicles was investigated. The coupled activities, ATP hydrolysis and proton pumping, were simultaneously supported only by Mg²⁺ or Mn²⁺. The presence of Ca²⁺ or Ba²⁺ did not significantly affect the coupled activities. The addition of Cd²⁺, Co²⁺, Cu²⁺, and Zn²⁺ inhibited both the hydrolysis of Mg-ATP and the proton transport. However, the inhibition of proton pumping was more pronounced. Based on equilibrium analysis, both ATP-complexed and free forms of these cations were inhibitory. Inhibition of the hydrolysis of Mg-ATP could be correlated to the concentrations of the ATP-complex of Zn. On the other hand, the free Cu²⁺ and Co²⁺ were effective in inhibiting hydrolysis. For proton pumping, the ATP complexes of Co²⁺, Cu²⁺, and Zn²⁺ were effective inhibitors. However, this inhibition could be further modulated by free Co²⁺, Cu²⁺, and Zn²⁺. While the equilibrium concentrations of Cd-ATP and free Cd²⁺ were not estimated, the total concentration of this cation needed to inhibit the coupled activities of the H⁺-ATPase was found to be in the range of 10 to 100 micromolars. The presence of free divalent cations also affected the structure of the lipid phase in tonoplast membrane as demonstrated by the changes of emission intensity and polarization of incorporated 1,6-diphenyl-1,3,5-hexatriene. The differential inhibition caused by these cations could be interpreted by interactions with the protogenic domain of the membrane as previously proposed in “indirect-link” mechanism.     

Male reproductive success in harem troops of hanuman langurs (Presbytis entellus)

Based on cross-sectional and longitudinal data collected in 1967–1988 by various observers, male reproductive success was studied in the Hanuman langurs of Jodhpur, India. The harem-structured social organization ensures a high degree of paternity certainty. Births occur throughout the year, with significant peaks and minima in March and November, respectively (n =398).The interbirth interval averages 16.7 months (n = 114).The duration of harem residencies varies between 3 days and ≥ 74.0 months, with a mean of 26.5 (n = 64). Harem holder replacements occur during all months of the year. No male achieves residency in more than one troop, suggesting that residency is associated with a distinct peak in the resource holding potential of a given male. Reproductive success among males varies considerably. Male mortality is high due to migration and intrasexual competition, leading to an adult sex ratio of 1:4.9. It is estimated that one-quarter of all adult males will never gain harem residency. Conceptions achieved outside harem residencies are so rare (4.7%) that a viable low-risk strategy, opting for longevity instead of harem residency, is unlikely. Tenure length has a stronger influence on male reproductive success than harem size because interbirth intervals are significantly shorter in small harems than in larger ones. It is assumed that females in one-male breeding structures compete for sperm and that such competition is more intense in larger harems.     

Modulation of cell surface heparan sulfate structure by growth of cells in the presence of chlorate

Swiss mouse 3T3 cells, when grown in the presence of 5 mM chlorate, an inhibitor of PAPS synthesis, produce heparan sulfate glycosaminoglycan chains containing only about 8% of the sulfate normally present and which have lost the ability to bind to fibronectin. These undersulfated chains are sensitive to nitrous acid at pH 4.5, indicating that many glucosaminyl residues have unsubstituted amino groups. The iduronic acid content of the heparan sulfate produced in the presence of chlorate is reduced to less than 7% as compared to the 36% in that from untreated cells. The chlorate-treated cells do not demonstrate any alterations in their growth control. However, the spreading behavior of these cells is altered to a flat rounded morphology compared to the more typical fibroblastic appearance of the untreated cell. The sulfation of chondroitin chains is also inhibited, but at a lower chlorate concentration which does not alter growth control or the spreading ability of the cells. These data indicate that (a) 3T3 cell surface heparan sulfate proteoglycan is not involved in growth control but may be involved in cell spreading, (b) the use of chlorate should be a valuable method for the study of the biosynthesis and structure/function relationships of sulfated glycosaminoglycans, and (c) the temporal sequence of the heparan sulfate chain modification reactions predicted from results of studies with cell-free extracts also operates in the cell.     

Signal transduction by membrane receptors in viable electropermeabilized cells: isoproterenol-stimulated cyclic AMP synthesis in C6 glioma cells

The activity of beta-adrenergic receptors at the plasma membrane level was investigated in viable, electropermeabilized C6 glioma cells. Electric field pulses were applied directly to the plated cells without any previous proteinase treatment. The affinity for isoproterenol and the density of the beta-adrenergic receptors, as judged from the number of [3H]CGP-12177 binding sites, were not affected by the electropermeabilization whereas the isoproterenol-stimulated cAMP accumulation was transiently impaired. This decrease in activity is due to an electropermeabilization-induced GTP leak. Normal activity could be obtained either by treating the cells by the electric field in a GTP-containing buffer, or by spontaneous recovery of the cells after the resealing of the plasma membrane, with a delay depending on the temperature. The activity of the receptors was not affected by the structural organization of the membrane associated to its electropermeabilization.     

Phenolic and mineral content of leaves influences decomposition in European forest ecosystems

Summary Factors influencing decomposition in European forests growing on different soils were studied in stands dominated by the European beechFagus sylvatica L. Phenolic contents of freshly fallen leaves ofF. sylvatica growing on nutrient-poor soils (acid sandy soil) were higher than those of similar leaves on nutrient-rich soils (calcareous mull soil). Analysis of fallen leaves of different ages showed rapid decay of phenolics during the first winter on the ground. After 1 year the phenolic content of leaves ofF. sylvatica growing on nutrient-poor soils was still twice as high as in similar leaves on nutrient-rich soils. Field and laboratory experiments showed that a major decomposer (Oniscus asellus, Isopoda) preferred leaves from trees on nutrient-rich soils. Mineral contents of leaves ofF. sylvatica growing on different soils differed: on rich soils leaves had higher contents of Ca, Mg, Na, and K. These elements are important nutrients for decomposers. The distribution of major decomposers reflects the mineral content of their diet, which in turn reflects soil type. Different rates of leaf turnover and nutrient turnover in different forest ecosystems (even when the same tree species is dominant) are due to the decomposing system, which is influenced by the phenolic and mineral contents of the leaves.