Signal peptidase I overproduction results in increased efficiencies of export and maturation of hybrid secretory proteins in Escherichia coli

Summary The effects of 25-fold overproduction ofEscherichia coli signal peptidase I (SPase I) on the processing kinetics of various (hybrid) secretory proteins, comprising fusions between signal sequence functions selected from theBacillus subtilis chromosome and the mature part of TEM-β-lactamase, were studied inE. coli. One precursor (pre[A2d]-β-lactamase) showed an enhanced processing rate, and consequently, a highly improved release of the mature enzyme into the periplasm. A minor fraction of a second hybrid precursor (pre[Al3i]-β-lactamase), which was not processed under standard conditions of SPase I synthesis, was shown to be processed under conditions of SPase I overproduction. However, this did not result in efficient release of the mature β-lactamase into the periplasm. In contrast, the processing rates of wild-type pre-β-lactamase and pre(A2)-β-lactamase, already high under standard conditions, were not detectably altered by SPase I overproduction. These results demonstrate that the availability of SPase I can be a limiting factor in protein export inE. coli, in particular with respect to (hybrid) precursor proteins showing low (SPase I) processing efficiencies.     

Trade-offs inDaphnia vertical migration strategies

Summary Planktonic animals performing diel vertical migration (DVM) experience a tradeoff between reduced mortality and reduced reproductive output due to lower food availability in their refuge. Models of DVM as an evolutionarily stable strategy predict that, under certain conditions, strategies of both migration and non-migration can coexist. Vertical profiles of animal abundances during day and night, however, do not allow any discrimination between the behaviour of individuals or subpopulations. We used length-body protein regressions as a measure of the nutritional state ofDaphnia to distinguish possible sub-populations differing in their migration strategy. An overwhelming part of the population migrated downwards during the day. However, the few daphnids in the epilimnion during the day had significantly higher protein content than the animals in the deep water, indicating that these daphnids did not migrate randomly but remained in the surface food-rich water all day. This shows that migrating animals gain no metabolic advantage over non-migrating ones.Supported by a F.P.U. grant (Spanish Goverment)     

Isolation and characterization of high-mobility-group proteins from maize

Chromosomal nonhistone high-mobility-group (HMG) proteins were purified from nuclei of maize (Zea mays L. cv. A619) endosperm and leaf tissue. Tissuespecific differences were observed in their polypeptide patterns, in in-vitro phosphorylation experiments with a casein-kinase type II, and by Western blot analysis with antisera against different HMG proteins. Gelfiltration chromatography demonstrated that maize HMG proteins occur as monomers. By measuring the capacity of the HMG proteins to bind to the 5 flanking region of a zein gene, the sensitivity of the proteins to different temperatures, salt concentrations and pH values was determined.Abbreviations EMSA electrophoretic-mobility-shift assay - FPLC fast protein liquid chromatography - HMG high-mobility group - kDa kilodaltons - PVDF polyvinylidenedifluoride - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis We would like to thank Mrs. E. Brutzer for excellent technical assistance. We are indebted to Mrs. M. Strecker and Dr. W. Bessler of the Institut für Immunbiologie, Freiburg, FRG, for the preparation of antisera and we gratefully acknowledge helpful discussions with Drs. T. Quayle, R. Grimm and U. Müller of this institute. This work was supported by grants from the Deutsche Forschungsgemeinschaft and the Fond der Chemischen Industrie.     

Reserve substances inPaxillus involutus sclerotia

Summary The ectomycorrhizal fungus,Paxillus involutus, produces sclerotia in culture. These can be induced to form on agar medium by exposing mycelium grown at 25°C to various temperatures between6°C and 15°C. Sclerotia formed at 10°C and above were large and covered with drops of exudate, while those formed at 6°C or 8°C were very small and did not produce an exudate. Mature sclerotia were bounded by a compact rind and contained abundant storage reserves. Histochemistry of the larger sclerotia showed large quantities of protein stored as protein bodies in the cytoplasm, lipid present as small droplets, glycogen granules stored in the cytoplasm and polyphosphate present as small granules in the cytoplasm and in the protein bodies. Energy dispersive X-ray microanalysis confirmed the presence of phosphate in the granules and was used to map its distribution throughout the sclerotium. The smaller sclerotia induced at 8°C and below on the same medium had the same basic structure and composition, but lacked the complex phenolic cell network found in large sclerotia, and had abundant extracellular polysaccharides. The rind was not well developed and these small sclerotia are interpreted to have been arrested at an early stage of development.     

Measurement of two-bond JCOHα coupling constants in proteins uniformly enriched with13C

Summary A simple E.COSY type technique is described for measurement of two-bond J_COH coupling constants in proteins that are uniformly enriched with¹³C. The method has been used to measure²J_COH for 132 residues in the proteins calmodulin and staphylococcal nuclease having non-overlapping H–C correlations. Measured²J_COH coupling constants fall in the 0 to –9.5 Hz range. A separate experiment, measuring the accuracy of these values, indicates a root-mean-square error of 1 Hz. Comparison of the J couplings with the dihedral back bone angles from crystallographic studies confirms a weak but statistically significant correlation between the dihedral angle and the magnitude of²J_COH, but also indicates that parameters other than have a significant effect on the value of the coupling.     

A method for determining overall protein fold from NMR distance restraints

Summary We describe a simple method for determining the overall fold of a polypeptide chain from NOE-derived distance restraints. The method uses a reduced representation consisting of two particles per residue, and a force field containing pseudo-bond and pseudo-angle terms, an electrostatic term, but no van der Waals or hard shell repulsive terms. The method is fast and robust, requiring relatively few distance restraints to approximate the correct fold, and the correct mirror image is readily determined. The method is easily implemented using commercially available molecular modeling software.     

Fractionated extraction and speciation of macronutrients from Scots pine and Norway spruce needles of different ages

Summary The relationship between proteins and the macroelements potassium, magnesium, calcium, sulphur and phosphorus was studied in homogenates of needles of different ages from Scots pine (Pinus sylvestris L.) and Norway spruce [Picea abies (L.) Karst.]. Complete extractions by acid digestion, protein extractions by a buffer-detergent and non-protein extractions by a buffer alone showed that most of the potassium and magnesium of the needles was soluble independent of the proteins. Only a minor part (50–60 ppm, dry weight) of the magnesium could be referred to the chlorophyll content of the needles. Both potassium and magnesium appeared independent of the protein gel filtration. This was also valid for the minor fraction of the total calcium content, which was extractable in a buffer. Heterogeneous calcium deposits are also suggested by extraction using a chelator (EGTA). Part of the buffer-soluble sulphur and phosphorus compounds occurred independently of solubilized proteins, and had complex distribution patterns after gel filtration, even outside the high molecular separation range. It is suggested that further analyses along the present lines, compared with conventional analyses on total extracts, may extend the usefulness of mineral nutrient analyses in plants.