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Biomedical subjects

E Schnepf

Publications and source records attributed to E Schnepf.

At least 19 recordsLinked to original sources
PubMed1998

Bacillus thuringiensis and its pesticidal crystal proteins.

During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism's pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Amino Acid Sequence↗
PubMed1998

Revision of the nomenclature for the Bacillus thuringiensis pesticidal crystal proteins.

The crystal proteins of Bacillus thuringiensis have been extensively studied because of their pesticidal properties and their high natural levels of production. The increasingly rapid characterization of new crystal protein genes, triggered by an effort to discover proteins with new pesticidal properties, has resulted in a variety of sequences and activities that no longer fit the original nomenclature system proposed in 1989. Bacillus thuringiensis pesticidal crystal protein (Cry and Cyt) nomenclature was initially based on insecticidal activity for the primary ranking criterion. Many exceptions to this systematic arrangement have become apparent, however, making the nomenclature system inconsistent. Additionally, the original nomenclature, with four activity-based primary ranks for 13 genes, did not anticipate the current 73 holotype sequences that form many more than the original four subgroups. A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed. Roman numerals have been exchanged for Arabic numerals in the primary rank (e.g., Cry1Aa) to better accommodate the large number of expected new sequences. In this proposal, 133 crystal proteins comprising 24 primary ranks are systematically arranged.

Bacillus thuringiensis↗
PubMed1990

Mobile and immobile endoplasmic reticulum in onion bulb epidermis cells: short- and long-term observations with a confocal laser scanning microscope.

The endoplasmic reticulum (ER) of onion bulb scale epidermis cells consists of long, tubular strands lying deep in the cytoplasm which move quickly and a less mobile peripheral network of tubules and cisternae that change in position, shape and size but that also have immobile, fixed, sites (IFSs). IFSs occur in junctions, at vertexes and at blind endings of tubules as well as at the edges and the surface of cisternae. They are regularly arranged in helicoidal rows and may be knot- or ring-like in structure. They become enlarged by treatment with oryzalin but not with colchicine. They persist for long times (for more than 30 min); together with pulling forces, the surface tension and other factors, they determine the configuration and motion of the peripheral network. New polygons of the network are mainly formed by the development of new tubules that become joined with other parts of the network. Polygons disappear by contraction and fusion of tubules. The inner, rapidly moving ER tubules remain connected with the peripheral network over longer distances by sliding junctions. Cytochalasin D causes an accumulation of the ER into patches, a fusion of tubules into cisternae and changes in shape, which indicate the loss of pulling forces. In contrast to animal cells (but like the movement of the inner tubular strands), the latter is dependent upon the actomyosin system; microtubules are not involved. Despite the differences in the organizing components, the peripheral ER in onion bulb scale epidermis cells and that of the borders of cultured animal cells are similar in morphology and motility.

Allium↗
PubMed1977

Chitinous fibrils in the lorica of the flagellate chrysophyte Poteriochromonas stipitata (syn. Ochromonas malhamensis).

Ordered microfibrils are formed on the membrane of the cytoplasmic tail of the alga Poteriochromonas after attachment to a substrate. The ultrastructure of native and extracted stalk fibrils was studied with electron microscope methods. In addition, the structural polysaccharide was characterized by hydrolyses, separation of the monomers by thin-layer chromatography, gas-liquid chromatography and amino acid analysis, and by X-ray diffraction. The alkali-resistant fibrils yielded mostly glucosamine upon extensive hydrolysis, and showed X-ray diffraction patterns similar to those of fugal chitin. It is concluded that the resistant core of the fibrils is chitinous.

Chitin↗