In vivo expression and mitochondrial targeting of yeast apoiso-1-cytochrome c fusion proteins.

To define the import pathway for apoiso-1-cytochrome c in vivo, the coding region for bacterial chloramphenicol acetyltransferase (CAT) or yeast copper metallothionein (CuMT) was fused to the carboxy terminus of the apoiso-1-cytochrome c (iso-1) coding region. When the resulting iso-1/CAT and iso-1/CuMT fusion proteins were individually expressed in Saccharomyces cerevisiae, they were specifically targeted to the mitochondria and protected from trypsin digestion. Although iso-1/CAT was accessible to heme modification, it remained membrane associated because of the folded conformation of the CAT domain. A small deletion disrupting CAT structure resulted in the translocation of the resulting fusion protein, iso-1/CAT delta, to the intermembrane space, where it functioned efficiently in respiratory electron transfer. Similarly, iso-1/CuMT was heme modified and nearly identical to iso-1 in its ability to support respiratory growth, indicating that the CuMT domain was compatible with translocation to the IMS. Inclusion of copper in the growth medium, which converts the loosely structured apo-CuMT to a tightly folded holo-CuMT, inhibited both heme attachment and respiratory growth without affecting mitochondrial targeting. Thus, by altering the folded conformation of the reporter moiety of these fusion proteins, it was possible to differentiate between those molecules arrested at the mitochondrial targeting step of the cytochrome c import pathway and those translocated to the intermembrane space. By replacing the heme-binding cysteine residues with serines, this system was used to demonstrate that the import requirement for heme attachment operated at the level of membrane translocation and not on mitochondrial targeting in vivo.     

Modelling growth responses of soil nitrifiers to additions of ammonium sulphate and ammonium chloride

Summary Following the addition of 0–75 mole N g^–1 as ammonium chloride or ammonium sulphate to a sandy loam soil the nitrate formed was measured daily for a period of 15–17 days. The nitrate produced as a function of time was described using the Monod equation for microbial growth. An optimisation technique is described for obtaining, from the nitrification time course data, the maximum specific growth rate, the affinity constantant and an index limited by the concentration of ammonium in soil solution. Additions of more than 7.3 moles N g^–1 soil as ammonium chloride were found to inhibit nitrification. The inhibition was interpreted as being caused by osmotic pressure or by chloride ion. A similar effect was not found with ammonium sulphate, because the salt concentration in the soil solution was restricted by the precipitation of calcium sulphate. The model developed was capable of accounting for nitrate production in the soil under non-steady state conditions of substrate concentrations and nitrifier biomass.     

A study of the mechanism of soil-phosphate uptake in relation to plant species

Summary The concept of plant available and unavailable soil phosphate has been examined by growing a range of plant species in soils well mixed with carrier free P³².It was found that although activities of 5–100 µC per kg soil caused changes in dry matter and P uptake, they had no influence on the specific activity per unit dose.Only small and agriculturally insignificant differences have been found in the proportion of soil P to added P³² taken up by the different species in the acid and neutral soils employed. It is considered that such differences as there are may be due to exchange of phosphate between seed and soil. Marked differences, however, occurred in the total phosphate absorbed by the crops.These results support the view that a fraction of the soil phosphate exists in a labile pool which will exchange with added P³² and will maintain a definite equilibrium potential in the soil solution. Plants do not appear to have a means of increasing significantly the size of the labile pool under the experimental conditions described. The disparity, however, between the total phosphate uptake especially in very deficient soils does suggest that certain species are more efficient than others in the absorption of soil phosphate at low potential.     

CNTF and LIF act on neuronal cells via shared signaling pathways that involve the IL-6 signal transducing receptor component gp130.

Ciliary neurotrophic factor (CNTF) has a variety of actions within the nervous system. While some of the actions of leukemia inhibitory factor (LIF) on neurons resemble those of CNTF, LIF also has broad actions outside of the nervous system that in many cases mimic those of interleukin-6 (IL-6). Comparison of the tyrosine phosphorylations and gene activations induced by CNTF and LIF in neuron cell lines reveals that they are indistinguishable and also very similar to signaling events that characterize LIF and IL-6 responses in hematopoietic cells. We provide a basis for the overlapping actions of these three factors by demonstrating that the shared CNTF and LIF signaling pathways involve the IL-6 signal transducing receptor component gp130. Thus, the receptor system for CNTF is surprisingly unlike those used by the nerve growth factor family of neurotrophic factors, but is instead related to those used by a subclass of hematopoietic cytokines.     

Microbial flora on doctors' white coats.

OBJECTIVE--To determine the level and type of microbial contamination present on the white coats of doctors in order to assess the risk of transmission of pathogenic micro-organisms by this route in a hospital setting. DESIGN--Cross sectional survey of the bacterial contamination of white coats in a general hospital. SETTING--East Birmingham Hospital, an urban general hospital with 800 beds. SUBJECTS--100 doctors of different grades and specialties. RESULTS--The cuffs and pockets of the coats were the most highly contaminated areas. The level of bacterial contamination did not vary with the length of time a coat had been in use, but it increased with the degree of usage by the individual doctor. Staphylococcus aureus was isolated from a quarter of the coats examined, more commonly from those belonging to doctors in surgical specialties than medical specialties. Pathogenic Gram negative bacilli and other pathogenic bacteria were not isolated. CONCLUSIONS--White coats are a potential source of cross infection, especially in surgical areas. Scrupulous hand washing should be observed before and after attending patients and it may be advisable to remove the white coat and put on a plastic apron before examining wounds. There is little microbiological reason for recommending a more frequent change of white coat than once a week, nor for excluding the wearing of white coats in non-clinical areas.     

Diffusion of phosphate to plant roots in soil

Summary A method is described for computing the theoretical distribution of solutes around a root with root hairs. The P concentration profile around the primary root of a rape seedling with root hairs, growing in a low-P soil, showed considerably greater depletions than predicted by this method, using the relationship between P in soil and in solution obtained from a desorption isotherm experiment. This suggests an enhanced release of soil P into solution in the rhizosphere.Soil Science Laboratory, Department of Agricultural Science, University of Oxford