Distribution of intermediate filaments in amphibian oxyntic cells

Summary Intermediate filaments of toad oxyntic cells were isolated and analysed by SDS-PAGE. The major proteins of the residue were identified as actin and a 51,000 dalton polypeptide. Immunological crossreactivity between toad oxyntic cell intermediate filament components and anti-prekeratin, was shown by double immunodiffusion tests and indirect immunofluorescence. The immunofluorescent decoration of oxyntic cells and the electron microscope images are coincident in locating the intermediate filaments mainly at the cortical and perinuclear basal zones. Furthermore, the cortical zone appears especially rich in prekeratin-like material at its adluminal third. This results in a cup-like structure that encloses the cell portion occupied by the tubulovesicular system, which does not contain intermediate filaments. The translocation of membranes occurring during the secretory cycle of the oxyntic cell, has been attributed to a system of contractile proteins. The disposition of the prekeratin-like material suggests a role for intermediate filaments in the generation of movement, produced by actin and myosin interaction, by providing a fixed plane for the anchoring of actin microfilaments.     

In-ovulo embryo culture and seedling development of cotton (Gossypium hirsutum L.)

A convenient and reliable method for culturing cotton embryos is needed to obtain interspecific hybrids of this genus. C.A. Beasley and I.P. Ting (Amer. J. Bot. 60, 130, 1973) developed a phytohormone-supplemented medium (BTP) upon which the growth of ovules was similar that of in situ ovules. This medium was examined for in-ovulo embryo culture. Although good ovule growth occurred on BTP no embryos developed to maturity. However, when the medium was supplemented with NH ₄ ⁺ , more than 50% of the ovules produced mature embryos, and many of these germinated precociously after 8–10 weeks of culture. After germination seedlings were established on a separate medium designed to give balanced root and shoot growth. Subsequently young plants could be transferred to pots for greenhouse culture.     

Binding of 4-methylumbelliferyl-galactosides to peanut agglutinin

The binding of 4-methylumbelliferyl-α-D-galactopyranoside, -β-D-galactopyranoside and -D-Galβ(1→3)DGalNac to peanut agglutinin was studied by fluorescence. Peanut agglutinin quenched the fluorescence intensity of 4-methylumbelliferyl-α-D-galactopyranoside but enhanced that of the two 4-methylumbelliferyl-β-galactosides. For α-D-galactopyranoside, the association constants measured at 4 and 25°C were 3.4 × 10³ and 1.7 × 10³ M^?1 respectively, and for D-Galβ(1→3)DGalNac, 1.5 × 10⁵ and 3.3 × 10⁴ M^?1. The binding enthalpies estimated from these values are consistent with the existence of extended sugar binding sites in the peanut agglutinin molecule.     

Engineering a Bacillus subtilis expression-secretion system with a strain deficient in six extracellular proteases.

We describe the development of an expression-secretion system in Bacillus subtilis to improve the quality and quantity of the secreted foreign proteins. This system consists of a strain (WB600) deficient in six extracellular proteases and a set of sacB-based expression vectors. With the inactivation of all six chromosomal genes encoding neutral protease A, subtilisin, extracellular protease, metalloprotease, bacillopeptidase F, and neutral protease B, WB600 showed only 0.32% of the wild-type extracellular protease activity. No residual protease activity could be detected when WB600 was cultured in the presence of 2 mM phenylmethylsulfonyl fluoride. By using TEM beta-lactamase as a model, we showed that WB600 can significantly improve the stability of the secreted enzyme. To further increase the production level we constructed an expression cassette carrying sacY, a sacB-specific regulatory gene. This gene was placed under the control of a strong, constitutively expressed promoter, P43. With this cassette in the expression vector, an 18-fold enhancement in beta-lactamase production was observed. An artificial operon, P43-sacY-degQ, was also constructed. However, only a partial additive enhancement effect (24-fold enhancement) was observed. Although degQ can stimulate the production of beta-lactamase in the system, its ability to increase the residual extracellular protease activity from WB600 limits its application. The use of the P43-sacY cassette and WB600 would be a better combination for producing intact foreign proteins in high yield.     

Reconstitution of sodium channels in large liposomes formed by the addition of acidic phospholipids and freeze-thaw sonication

Phosphatidylcholine (PC) alone or with phosphatidylethanolamine (PE) are sufficient for the reconstitution of Na+ channels in planar lipid bilayers. However, when Na+ channels were first reconstituted into liposomes using the freeze-thaw-sonication method, addition of acidic phospholipids, such as phosphatidylserine (PS), to the neutral phospholipids was necessary to obtain a significant toxin-modulated 22Na uptake. To further investigate the acidic phospholipid effect on reconstitution into liposomes, Na+ channels purified from Electrophorus electricus electrocytes were reconstituted into liposomes of different composition by freeze-thaw sonication and the effect of batrachotoxin and tetrodotoxin on the 22Na flux was measured. The results revealed that, under our experimental conditions, the presence of an acidic phospholipid was also necessary to obtain a significant neurotoxin-modulated 22Na influx. Though neurotoxin-modulated 22Na fluxes have been reported in proteoliposomes made with purified Na+ channels and PC alone, the 22Na fluxes were smaller than those found using lipid mixtures containing acidic phospholipids. Electron microscopy of negatively stained proteoliposomes prepared with PC, PC/PS (1:1 molar ratio), and PS revealed that the acidic phospholipid increases the size of the reconstituted proteoliposomes. The increment in size caused by the acidic phospholipid, due to the associated increase in internal volume for 22Na uptake and in area for Na+ channel incorporation, appears to be responsible for the large neurotoxin-modulated 22Na fluxes observed.     

DNA binding and dimerization determinants for thyroid hormone receptor alpha and its interaction with a nuclear protein.

The gel retardation assay was used to analyze the role of the thyroid hormone receptor alpha (TR alpha) ligand-binding domain (LBD) in controlling receptor interaction with a thyroid hormone responsive element (TRE). While wild type receptor TR alpha binds to the TRE mainly as monomer, deletion of 85 amino acids from its C-terminus results in a mutant receptor with enhanced DNA binding that forms several slow mobility complexes as revealed by gel retardation assay. Receptor deletion mutants that lack most of the LBD show significantly elevated DNA binding and are still able to bind to DNA as two complexes. Thus, the C-terminal end of TR alpha appears to interfere with the dimerization/oligomerization function and DNA binding of TR alpha. All C-terminal deletion mutants have lost their T3-responsive activator function, but some show constitutive activity. Nuclear factor from several cell lines, including CV-1, F9, and GC cells, interacts with TR alpha receptor to form a larger molecular weight complex as determined by gel retardation assay. This factor could not be detected in HeLatk- cells, where TR alpha does not activate a TRE-containing reporter gene. The nuclear factor is heat sensitive and does not bind to TRE itself but can interact with TR alpha in the absence of DNA. Deletion analysis demonstrates that the leucine zipper-like sequence located in the LBD of TR alpha is involved in this interaction. Together, our data suggest that TR alpha contains a dimerization function outside the LBD which is inhibited by the carboxy-terminal region, while the leucine zipper-like sequence in the LBD is required for interaction with a nuclear factor.     

Chromosomal localization of zein genes by in situ hybridization in Zea mays

Summary In order to localize the genes coding for zein, the major storage protein of maize endosperm, zein ¹²⁵I-mRNA and ³H-cDNA labelled at high specific activity were used for in situ hybridization on heterozygous interchanges and paracentric inversions of the KYS strain of Zea mays. The analysis of the diplotene-metaphase I microsporocytes indicated the presence of zein structural genes on the long arm of chromosomes 4 and 5, the short arm of chromosome 7 and the distal segment of the long arm of chromosome 10. The two hybridization sites on chromosomes 7 and 10 are found near opaque-2 and opaque-7 loci which are known to regulate zein synthesis. The present data are discussed in relation to results obtained by other authors using genetical mapping of zein genes.     

Properties and biosynthetic connection of the nucleotide pyrophosphatases of rat liver plasma membrane and endoplasmic reticulum

The detergent-solubilized nucleotide pyrophosphatases of the rat liver plasma membrane and endoplasmic reticulum fractions were purified by lectin affinity chromatography. They have the same molecular mass of 148 000 dalton; their catalytic properties are also very similar and correspond to those of the trypsin-solubilized activities from the same membrane preparations. Pulse-chase experiments on isolated perfused livers using [3H]leucine indicated different labelling kinetics of the proteins isolated from plasma membrane and endoplasmic reticulum. The plasma membrane enzyme became only slightly labelled in the presence of 100 microM vinblastine. The data support a precursor-product relationship of the nucleotide pyrophosphatases from endoplasmic reticulum and plasma membrane.     

Cytochemistry and freeze-fracture of membranes isolated from the electrocyte of Electrophorus electricus (L.)

Summary Membranes were isolated from the main electric organ of Electrophorus electricus and studied by means of cytochemistry and freezefracture. The membrane fractions consisted of vesicles inside-in as determined by localization of anionic sites using colloidal iron and cationized ferritin particles. The anionic sites were not homogeneously distributed on the surface of the vesicle. Freeze-fracture showed the presence of intramembranous particles associated with either protoplasmic (P) or extracellular (E) faces of the membrane. Regions of the membrane without particles were observed. The results are discussed in relation to the existence of association between intramembranous particles and membrane receptors.For all correspondence