Bacteriophage-resistant mutants of Bacillus thuringiensis with decreased virulence in pupae of Hyalophora cecropia

Starting from a crystal-negative parental strain of Bacillus thuringiensis, we isolated certain bacteriophage-resistant mutants which showed decreased virulence in pupae of the cecropia moth (Hyalophora cecropia). These strains (class I mutants) were highly pleiotropic and showed resistance to seven or eight different phages, sensitivity to methicillin, and loss of flagella. They were also more sensitive to cecropia immune hemolymph in vitro. In addition, the export of at least three proteins was reduced. Revertants (class II mutants) were sensitive to phages, virulent, and resistant to penicillin derivatives. One class II mutant was a complete revertant in all properties examined. The other class II mutant was an incomplete revertant still susceptible to immune hemolymph and with repressed export of proteins. Virulence was not coupled to phage resistance as such or to lack of flagella because other mutants affected in these properties were virulent. Other factors which could be excluded as causes of virulence were production of extracellular protease and hemolysin.     

Lycorine: a eukaryotic termination inhibitor?

The effect of the alkaloid lycorine on viral protein synthesis was studied in poliovirus-infected HeLa cells. The incorporation of [3H]leucine was inhibited by lycorine in a dose-dependent way, although lycorine never completely abolished translation. Using polyacrylamide gel electrophoresis, the viral proteins were identified as derived from the P1 (5' terminal), P2 (middle), or P3 (3' terminal) region of the poliovirus translation unit. The residual labeling of viral proteins in the presence of lycorine was mainly due to synthesis of P1 proteins and slightly less to P2 proteins, while virtually no P3-derived proteins were made. It is suggested that lycorine may act at the level of termination.     

Two novel matrix proteins isolated from articular cartilage show wide distributions among connective tissues

Two proteins of Mr = 58,000 and 59,000, respectively, were purified from 4 M guanidinium chloride extracts of articular cartilage by dissociative CsCl-density gradient centrifugation followed by gel chromatography on Sephadex G-200 and ion exchange chromatography on DEAE-cellulose. The two proteins differ in ionic properties and only the one with Mr = 59,000 bound to the ion exchanger. Although the two proteins showed dissimilar peptide patterns after proteolysis, their amino acid composition was similar, with very high contents of leucine and aspartic acid/asparagine. The two proteins showed no cross-reactivity in radioimmunoassays. By use of these assays, the proteins were demonstrated in extracts of most connective tissues, with high contents of about 0.1% of tissue wet weight determined in several types of cartilage. Among the non-cartilage connective tissues, tendon and sclera had the highest contents of the proteins, i.e. about 0.1% of the tissue wet weight. Bone extracts, on the other hand, contained insignificant amounts of the proteins. Only the Mr = 59,000 protein was detected in serum, its concentration being about 33 micrograms/l. Both proteins were shown to be localized in the extracellular matrix of cartilage, predominantly in the territorial matrix, by using indirect immunofluorescence.     

Lack of correlation between extensive accumulation of bisnucleoside polyphosphates and the heat-shock response in eukaryotic cells

The accumulation in large amounts of bisnucleoside polyphosphates (Ap4X) after heat shock in Xenopus laevis oocytes or cultured hepatoma cells (HTC cells) is observed after exposure to temperatures of 45 degrees C or higher. The accumulation is a transient phenomenon, with the collapse in cellular ATP concentration severely affecting the rate of synthesis of Ap4X, allowing degrading activities to empty the pool of these compounds under prolonged heat shock. This accumulation of Ap4X to high levels, compared to the basic content, is only observed under conditions leading to irreversible damage, ultimately resulting in the death of the cell. It is shown that the increase in Ap4X after hyperthermia is due to the partial or almost complete inhibition of their degradation pathways, rather than to a stimulation of their rate of synthesis. Finally, the synthesis of heat-shock proteins could be observed under conditions which do not lead to important accumulation of Ap4X, therefore ruling out the possibility that these adenylylated nucleotides would behave as chemical signals ("alarmones") triggering the synthesis of heat-shock proteins. Nevertheless, on the basis of our earlier results (Guédon, G., Sovia, D., Ebel, J. P., Befort, D., and Remy, P. (1985) Embo J. 4, 3743-3749), it cannot be excluded that Ap4X might play a role in the regulation of the heat-shock response; this would, however, rely on variations in Ap4X concentrations which do not exceed a factor of 2.     

Isolation of cDNA clones and complete amino acid sequence of human erythrocyte glycophorin C

Two cDNA clones for glycophorin C, a transmembrane glycoprotein of the human erythrocyte which carries the blood group Gerbich antigens, have been isolated from a human reticulocyte cDNA library. The clones were identified with a mixture of 32 oligonucleotide probes (14-mer) which have been synthetized according to the amino acid sequence Asp-Pro-Gly-Met-Ala present in the N-terminal tryptic peptide of the molecule. The primary structure of glycophorin C deduced from the nucleotide sequence of the 460 base-pair insert of the pGCW5 clone indicates that the complete protein is a single polypeptide chain of 128 amino acids clearly organized in three distinct domains. The N-terminal part (residues 1-57, approximately) which is N- and O-glycosylated is connected to a hydrophilic C-terminal domain (residues 82-128, approximately) containing 4 tyrosine residues by a hydrophobic stretch of nonpolar amino acids (residues 58-81, approximately) probably interacting with the membrane lipids and permitting the whole molecule to span the lipid bilayer. Northern blot analysis using a 265-base-pair restriction fragment obtained by DdeI digestion of the inserted DNA shows that the glycophorin C mRNA from human erythroblasts is approximately 1.4 kilobases long and is present in the human fetal liver and the human K562 and HEL cell lines which exhibit erythroid features. The glycophorin C mRNA, however, is absent from adult liver and lymphocytes, indicating that this protein represents a new erythrocyte-specific probe which might be useful to study erythroid differentiation.     

Physical and surface properties of insect apolipophorin III

Apolipophorin III (apoLp-III) from Manduca sexta has a molecular weight of 18,100. Based on its hydrodynamic properties (sedimentation and diffusion coefficients, frictional ratio, intrinsic viscosity) and its behavior during gel permeation chromatography, we concluded that apoLp-III is a prolate ellipsoid with an axial ratio of about 3. The circular dichroic spectrum of apoLp-III suggests that the protein contains approximately 50% alpha-helix. At the air-water interface, apoLp-III forms a monolayer which is gaseous at surface pressures less than or equal to 1 dyne/cm. The isotherm of this phase yields an excluded molecular area of 3800 A2/molecule (23 A2/amino acid). At a surface pressure of 22.1 dynes/cm, the monolayer undergoes a phase transition reminiscent of a first-order phase transition of pure lipids. The monolayer can be compressed in this surface pressure range to an area per molecule of 480 A2 (2.9 A2/amino acid). Since a globular protein of molecular weight 18,100 could occupy an area of only about 2000 A2 when bound to a surface, it is suggested that in the expanded state, apoLp-III must unfold on the surface, whereas in the compressed state, the molecule is oriented with its minor axis parallel to the water surface. ApoLp-III binds with high affinity (Kd = 1.9 X 10(-7)M) to both phosphatidylcholine- and diacylglycerol-coated polystyrene beads. All of these results are consistent with the proposal that apoLp-III plays a key role in increasing the capacity of the insect lipoprotein, lipophorin, to transport diacylglycerol by stabilizing the increment of lipid-water interface that results from diacylglycerol uptake.     

Epiphyseal-based designs for tibial plateau components--II. Stress analysis in the sagittal plane

A two-dimensional, finite element study was undertaken to establish the stresses in the proximal tibia before and after total knee arthroplasty. Equivalent-thickness models in a sagittal plane were created for the natural, proximal tibia and for the proximal tibia with two different types of tibial plateau components. All components simulated bony ingrowth fixation, i.e. no cement layer existed between component and bone. In addition, the interface between component and bone was assumed to be intimately connected, representing complete bony ingrowth and a rigid state of fixation. Two load cases were considered: a joint reaction force acting in conjunction with a patellar ligament force, simulating the knee at 40 degrees of flexion; and a joint reaction force directed along the long axis of the tibia. For the natural tibia model, the pattern of principal stresses for loadcase 1 more closely corresponds to the epiphyseal plate geometry and trabecular morphology than do the principal stress patterns for loadcase 2. Judging from the distribution of principal stresses, loadcase 1 represents a more severe test of implant design than does loadcase 2. The model of the component with a peg predicted that the trabecular bone near the tip of the peg will experience higher than normal stresses, while the bone stresses near the posterior aspect adjacent to the metal tray will be reduced. A component without pegs that incorporates a posterior chamfer and an anterior lip lead to stress distributions closer to those existing in the natural tibia. The interface geometry for this design is based upon the contour of the epiphyseal plate.     

Alpha-thrombin-induced inositol phosphate formation in G0-arrested and cycling hamster lung fibroblasts: evidence for a protein kinase C-mediated desensitization response

In resting Chinese hamster fibroblasts (CCL39) alpha-thrombin rapidly induces the breakdown of phosphoinositides. Accumulation of inositol phosphates (IP), measured in the presence of Li+, is detectable within 5s (seconds) of thrombin stimulation. Formation of inositol tris- and bisphosphates slightly precedes that of inositol monophosphate, indicating that thrombin activates primarily the phospholipase C-mediated generation of inositol trisphosphate from phosphatidylinositol 4,5-bisphosphate. Initial rates of IP production increase with thrombin concentration, with no apparent saturability over the range 10(-4)-10 U/ml. Thrombin-induced phosphoinositide hydrolysis rapidly desensitizes (t1/2 less than 5 min), but a residual activity, corresponding to about 10% of the initial stimulation is sustained for at least 9 h, in contrast with the undetectable activity of G0-arrested cells. This apparent desensitization may be due to a feedback regulation by protein kinase C, since pretreatment with the phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) markedly inhibits (by up to 70%) subsequent thrombin-induced inositol phosphate formation. Conversely, growth factor deprivation of CCL39 cells results in a progressive increase of thrombin-induced phosphoinositide hydrolysis, from the very low level of exponentially growing cells to the maximal level of G0-arrested cells. This "up regulation" was found maximal in A51, a very well growth-arrested CCL39 derivative, and reduced or virtually abolished in two tumoral and growth factor-relaxed derivatives of CCL39. Although preliminary, this observation suggests that a persistent activation of phosphatidyl inositol breakdown might operate in variants selected for autonomous growth.