A traffic-activated Golgi-based signalling circuit coordinates the secretory pathway

As with other complex cellular functions, intracellular membrane transport involves the coordinated engagement of a series of organelles and machineries; however, the molecular basis of this coordination is unknown. Here we describe a Golgi-based signalling system that is activated by traffic and is involved in monitoring and balancing trafficking rates into and out of the Golgi complex. We provide evidence that the traffic signal is due to protein chaperones that leave the endoplasmic reticulum and reach the Golgi complex where they bind to the KDEL receptor. This initiates a signalling reaction that includes the activation of a Golgi pool of Src kinases and a phosphorylation cascade that in turn activates intra-Golgi trafficking, thereby maintaining the dynamic equilibrium of the Golgi complex. The concepts emerging from this study should help to understand the control circuits that coordinate high-order cellular functions.     

Genetic polymorphism of the kappa-casein gene in Brazilian cattle

Frequencies of kappa-casein gene alleles were determined in 1316 animals from the Brazilian Bos indicus genetic groups (Sindhi cows, Gyr sires, Gyr cows, Guzerat sires, Guzerat cows, Nellore sires, and Gyr x Holstein crossbreds) by means of polymerase chain reaction-restriction fragment length polymorphism analysis using two independent restriction nucleases (Hinf I and HaeIII). The genotyping of kappa-casein alleles (A and B) is of practical importance, since the B allele is found to correlate with commercially valuable parameters of cheese yielding efficiency. The frequencies of the B allele of kappa-casein among breeds ranged from 0.01 to 0.30. The Sindhi breed had the highest frequency for the B allele (0.30), while the frequencies of this allele in other breeds ranged from 0.01 to 0.18. A wide variation in the B allele frequency among B. indicus breeds was found suggesting that molecular selection for animals carrying the B allele could impact breeding programs for dairy production.     

Phytoextraction: an assessment of biogeochemical and economic viability

Phytoextraction describes the use of plants to remove metals and other contaminants from soils. This low-cost technology has potential for the in situ remediation of large areas of contaminated land. Despite more than 10 years of intensive research on the subject, very few commercial phytoextraction operations have been realised. Here, we investigate the viability of phytoextraction as an effective land-treatment technology. A Decision Support System (DSS) was developed to predict the effect of phytoextraction on soil metal concentration and distribution, as well as the economic feasibility of the process in comparison to either inaction or the best alternative technology. Changes in soil metal concentration are mechanistically predicted on the basis of plant water use, metal concentration in soil solution, soil density, plant root distribution and our so-called root-absorption factor. The root-absorption factor is a `lumped parameter' describing the xylem/soil solution metal concentration quotient. Phytoextraction is considered to be a viable option if it can satisfy environmental regulations and simultaneously be shown to be the most cost-effective technology, either alone, or in combination with other remediation technologies. To date, commercial phytoextraction has been constrained by the expectation that site remediation should be achieved in a time comparable to other clean-up technologies. However, if phytoextraction could be combined with a profit making operation such as forestry, then this time constraint, which has often been considered to be the Achilles heel of phytoextraction, may be less important.     

Comparative cytotoxicity of fumonisin B1 in two cell lines derived from normal human bronchial epithelial cells using four distinct bioassay techniques

This study focuses on the cytotoxic effects of fumonisin B₁ (FB₁) on both immortalised and immortalised and subsequently transfected normal human bronchial epithelial (NHBE) cells of human origin using four bioassays. While the MTT, Neutral Red and hexosaminidase colorimetric assays showed little difference between the toxic effects on the two related cell lines, the clonogenic assay, measuring cell survival and proliferation, indicated that FB₁ had a more toxic effect on the nontransfected cells. This kind ofin vitro approach using cells which retain many characteristics of normal cell growth and differentiation can go some way to developing evaluation models for food safety in the case of mycotoxin contamination without resorting totally to whole animal testing. Nevertheless, one or two cytotoxicity tests may be inadequate for a complete appraisal of toxic potential: rather, as wide a range of methodologies as feasible should be employed initially before meaningful conclusions may be drawn.     

Studies of DNA dumbbells. VI. Analysis of optical melting curves of dumbbells with a sixteen-base pair duplex stem and end-loops of variable size and sequence

Optical melting curves of 22 DNA dumbbells with the 16-base pair duplex sequence 5′-G-C-A-T-C-A-T-C-G-A-T-G-A-T-G-C-3′ linked on both ends by single-strand loops of A_t or C_t sequences (˛ = 2, 3, 4, 6, 8, 10, 14), T_t sequences (˛ = 2, 3, 4, 6, 8, 10), and G_t sequences (t = 2, 4) were measured in phosphate buffered solvents containing 30, 70, and 120 mM Na⁺. For dumbbells with loops comprised of at least three nucleotides, stability is inversely proportional to end-loop size. Dumbbells with loops comprised of only two nucleotide bases generally have lower stabilities than dumbbells with three base nucleotide loops. Experimental melting curves were analyzed in terms of the numerically exact (multistate) statistical thermodynamic model of DNA dumbbell melting previously described (T. M. Paner, M. Amaratunga & A. S. Benight (1992), Biopolymers 32, 881). Theoretically calculated melting curves were fitted to experimental curves by simultaneously adjusting model parameters representing statistical weights of intramolecular hairpin loop and single-strand circle states. The systematically determined empirical parameters provided evaluations of the energetics of hairpin loop formation as a function of loop size, sequence, and salt environment. Values of the free energies of hairpin loop formation ΔG_loop(n > t) and single-strand circles, ΔG_cir(N) as a function of end-loop size, t = 2-14, circle size, N = 32 + 2_t, and loop sequence were obtained. These quantities were found to depend on end-loop size but not loop sequence. Their empirically determined values also varied with solvent ionic strength. Analytical expressions for the partition function Q(T) of the dumbbells were evaluated using the empirically evaluated best-fit loop parameters. From Q(T), the melting transition enthalpy ΔH, entropy ΔS, and free energy ΔG, were evaluated for the dumbbells as a function of end-loop size, sequence, and [Na⁺]. Since the multistate analysis is based on the numerically exact model, and considers a statistically significant number of theoretically possible partially melted states, it does not require prior assumptions regarding the nature of the melting transition, i.e., whether or not it occurs in a two-state manner. For comparison with the multistate analysis, thermodynamic transition parameters were also evaluated directly from experimental melting curves assuming a two-state transition and using the graphical van't Hoff analysis. Comparisons between results of the multistate and two-state analyses suggested dumbbells with loops comprised of six or fewer residues melted in a two-state manner, while the melting processes for dumbbells with larger end-loops deviate from two-state behavior.Dependence of thermodynamic parameters on[Na⁺] as a function of loop size suggests single-strand end-loops have different counterion binding properties than the melted circle. Results are compared with those obtained in an earlier study of dumbbells with the slightly different stem sequence 5'-G-C-A-T-A-G-A-T-G-A-G-A-A-T-G-C-3' linked on the ends by T loops (˛ = 2,3,4,6,8,10,14).© 1996 John Wiley &Sons, Inc.