Behaviour of bacterial division protein FtsZ under a monolayer with phospholipid domains

Assembly of the tubulin-like protein FtsZ at or near the cytoplasmic membrane is one of the earliest steps in division of bacteria such as Escherichia coli. Exactly what constitutes the site at which FtsZ acts is less clear. To investigate the influence of the membrane phospholipids on FtsZ localization and assembly, we have elaborated with the Langmuir technique a two-lipid monolayer made of dilauryl-phosphatidylethanolamine (DLPE) and dipalmitoyl-phosphatidylglycerol (DPPG). This monolayer comprised stable condensed domains in an expanded continuous phase. In the presence of GTP, FtsZ assembly disrupts the condensed domains within 5 min. After several hours, with or without GTP, FtsZ assembled into large aggregates at the domain interface. We suggest that the GTP-induced polymerization of FtsZ is coupled to the association of FtsZ protofilaments with domain interfaces.     

Statistical Modelling of Meiotic Configurations in Tetraploids

This paper studies the modelling of linkage between chromosomes in tetraploids. A general model based on the assumptions of Kimber and Alonso (1981) is presented. It depends on the “elementary probabilities” associated with the different configurations of pairing of the four chromosome arms depending on the same quadruplet. Because of the incomplete information about these pairings given by the microscopic observation of the cells, some problems about the identifiability of the parameters arise. We will present a set of the most general parameters that are identifiable and we will describe the set of the elementary probabilities that correspond to these parameters. Finally, we shall discuss some various possible sub-models.     

Antibacterial and hemolytic activities of linenscin OC2, a hydrophobic substance produced by Brevibacterium linens OC2

Linenscin OC2 is an antibacterial substance produced by the orange cheese coryneform bacterium Brevibacterium linens OC2. It inhibits the growth of Gram-positive bacteria but it is inactive against Gram-negative bacteria. The intact outer membrane of Gram-negative bacteria was shown to be an effective permeability barrier against linenscin OC2. At high dosage the effect of linenscin OC2 was bacteriolytic on Listeria innocua. Bacteriostasis was observed at low dosage and peptidoglycan biosynthesis was affected at an early step upstream of the UDP-N-acetylglucosamine. Hemolytic activity of this substance on sheep erythrocytes suggested a common mode of action on prokaryotic and eukaryotic cells. It also suggested that the cytoplasmic membrane might be the primary target of linenscin OC2.     

Human umbilical vein endothelial cells express high affinity receptors for factor Xa

The binding of [¹²⁵I]-factor Xa to human umbilical vein endothelial cell (HUVEC) monolayers was studied. At 7°C, [¹²⁵I]-factor Xa bound to a single class of binding sites with a dissociation constant value of 6.6 ± 0.8 nM and a binding site density of 57,460 ± 5,200 sites/cell (n = 3). Association and dissociation kinetics were of a pseudo-first order and gave association and dissociation rate constant values of 0.15 × 10⁶ M^-1 s^-1 and 4.0 × 10^-4 s^-1, respectively. [¹²⁵I]-factor Xa binding was inhibited by factor Xa but was not affected by factor X, thrombin or monoclonal antibodies against factor V, antithrombin-III or tissue factor pathway inhibitor (TFPI) but was inhibited by an antibody specific for the effector cell protease receptor-1 (EPR-1), a well-known receptor of factor Xa on various cell types. [¹²⁵I]-factor Xa binding to HUVEC was not affected by various inhibitors of factor Xa such as DX 9065, pentasaccharide-antithrombin-III or TFPI. Factor Xa increased intracellular free calcium levels and phosphoinositide turnover in endothelial cells and, when added to HUVEC in culture, factor Xa was a potent mitogen, stimulating an increase in cell number at a 0.3 to 100 nM concentration. HUVEC-bound factor Xa promoted prothrombin activation in the presence of factor Va only. This effect was inhibited by both indirect and direct inhibitors of factor Xa. These findings indicate that HUVEC express functional high affinity receptors for factor Xa, related to EPR-1, which may be of importance in the regulation of coagulation and homeostasis of the vascular wall. J. Cell. Physiol. 172:36–43, 1997. © 1997 Wiley-Liss, Inc.     

Relationship between rate of crop growth at date of fertiliser N application and fate of fertiliser N applied to winter wheat

To investigate the relationship between the timing of fertiliser N applications and the N use efficiency of wheat, three field experiments with ¹⁵N were set up on winter wheat, on three different soils in France. Different crop N demands on the day of fertiliser application were obtained by varying either crop densities or date of fertiliser application. Labelled ¹⁵NH₄ ¹⁵NO₃ was applied at tillering and during stem elongation. The ¹⁵N recovered from plant and soil at different dates after ¹⁵N addition and at maturity of wheat was measured. The fate of fertiliser N was rapidly determined, most of the fertiliser N accumulated in the wheat at maturity having been taken up within a few days of application. ¹⁵N recovery by the crop at final harvest (%) varied greatly (19–55% N applied) according to crop density, soil type and date of application. It was linearly related to the instantaneous crop growth rate calculated at the day of ¹⁵N application. The amount of fertiliser N immobilised in the soil was constant at 20 kg N ha⁻¹, for all soil types and crop densities. Because residual mineral ¹⁵N in the soil at harvest was negligible and immobilisation was constant, the level of total ¹⁵N measured in the different N pools (soil+plant) reflected the% ¹⁵N uptake by the plant. There was consequently a negative linear relationship between the percentage of ¹⁵N not recovered for measurement, and crop growth rate (i.e. crop N demand) at date of fertiliser application. These results suggest that crop N demand at the time of N application determines the ability of the crop to compete for N with other processes, and may be a major factor determining the division of N between soil and crop. This revised version was published online in June 2006 with corrections to the Cover Date.     

Comparison of promoters suitable for regulated overexpression of β-galactosidase in the alkane-utilizing yeastYarrowia lipolytica

Promoters of the genesG3P, ICL1, POT1, POX1, POX2 andPOX5 of the yeastY. lipolytica were studied in respect to their regulations and activities during growth on different carbon sources. The aim of this study was to select suitable promoters for high expression of heterologous genes in this yeast. For this purpose the promoters were fused with the reporter genelacZ ofE. coli and integrated as single copies into the genome ofY. lipolytica strain PO1d. The measurement of expressed activities of β-galactosidase revealed thatpICL1, pPOX2 andpPOT1 are the strongest regulable promoters available forY. lipolytica, at present.pPOX2 andpPOT4 were highly induced during growth on oleic acid and were completely repressed by glucose and glycerol.pICL1 was strongly inducible by ethanol besides alkanes and fatty acids, however, not completely repressible by glucose or glycerol. Ricinoleic acid methyl ester appeared as a very strong inducer forpPOT1 andpPOX2, in spite of that it inhibited growth ofY. lipolytica transformants.     

Long-term dynamics of a tropical savanna bird community

Complete two-month censuses of diurnal raptors and strip transect counts of other bird species were compared between 1968–1972 and 1996 to assess changes in the bird community of a 2700ha guinean savanna in Ivory Coast. Among 117 non-raptor species recorded at least once on the transects, 25 mostly uncommon species were absent in 1996 (but only two of them were likely to be extinct in the study area), 4 were first seen in 1996, 14 decreased and 4 increased significantly. All six large forest raptors and resident savanna eagles disappeared before the mid-1980s. Among the 12 remaining breeding raptors, 4 species increased (including the 2 seasonal migrants), 4 species remained stable (including the 2 forest accipiters) and 4 species decreased, but not significantly (including the 2 largest taxa). All 14 non-breeding raptors (Palearctic and African migrants) remained stable or increased. With on average 63 breeding pairs per 1000ha, this area still supports one of the highest densities of diurnal raptors ever recorded. The geographic distributions, seasonal movements and ecological requirements of species involved suggest the most likely origin of specific changes observed. They were attributed, in roughly similar proportion, to: (i) decreasing rainfall (southward shifts leading to appearance or increase of some resident or migrant species); (ii) deforestation, agricultural development and hunting pressure around the reserve (extinction of larger species following habitat fragmentation or degradation, increase of some species); and (iii) habitat modifications inside the reserve (increasing tree cover, invasion of dense thickets, illegal exploitation of palms). The overall community of this small protected area, however, exhibited a remarkable stability during the last 30 years, in spite of dramatic habitat changes outside its limits.