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A specific premessenger ribonucleoprotein (RNP) particle in the salivary glands of the dipteran Chironomus tentans was studied with electron microscope tomography during translocation from the cell nucleus to the cytoplasm. The RNP particle consists of a thin RNP fiber tightly folded into a ribbon, which is bent into a ring-like structure. Upon(More)
Nephrin is a key functional component of the slit diaphragm, the structurally unresolved molecular filter in renal glomerular capillaries. Abnormal nephrin or its absence results in severe proteinuria and loss of the slit diaphragm. The diaphragm is a thin extracellular membrane spanning the approximately 40-nm-wide filtration slit between podocyte foot(More)
The Balbiani ring 3 (BR3) gene contains 38 introns, and more than half of them are co-transcriptionally excised. We have determined the in situ structure of the active BR3 gene by electron tomography. Each of the 20-25 nascent transcripts on the gene is present together with splicing factors and the RNA polymerase II in a nascent transcript and splicing(More)
We have developed an objective, quantitative, and general algorithm to improve the fidelity of three-dimensional reconstructions made from electron micrographs while at the same time filtering much of the noise present in the recorded data. The new technique is called constrained maximum entropy tomography (COMET). The essence of the method is that it will(More)
The transport of Balbiani ring (BR) premessenger RNP particles in the larval salivary gland cells of the dipteran Chironomus tentans can be followed using electron microscopy. A BR RNP particle consists of an RNP ribbon bent into a ringlike structure. Upon translocation through the nuclear pore complex (NPC), the ribbon is straightened and enters the(More)
Electron microscope tomography has been used to refine the structural analysis of individual RNP particles synthesized on Balbiani ring genes in Chironomus tentans. The spherical particles have a diameter of 500 A and are composed of a thick RNP ribbon bent into an asymmetrical, four-domain, ring-like configuration. The first domain, containing the 5' end(More)
Using electron tomography, we have analyzed whether the Balbiani ring (BR) pre-mRNP particles in transit from the gene to the nuclear pore complex (NPC) are bound to any structure that could impair free diffusion through the nucleoplasm. We show that one-third of the BR particles are in contact with thin connecting fibers (CFs), which in some cases merge(More)
The highly ordered central region of the synaptonemal complex (SC) in Blaps cribrosa has recently been studied by electron microscope tomography (EMT), and a simple three-dimensional model presented. Using the same experimental approach we have now compared the central region in Blaps with the central regions in Drosophila melanogaster and rat. In all three(More)
Electron tomography of vitreous tissue sections (tissue TOVIS) allows the study of the three-dimensional structure of molecular complexes in a near-native cellular context. Its usage is, however, limited by an unfortunate combination of noisy and incomplete data, by a technically demanding sample preparation procedure, and by a disposition for specimen(More)
Cell adhesion molecules (CAMs) sense the extracellular microenvironment and transmit signals to the intracellular compartment. In this investigation, we addressed the mechanism of signal generation by ectodomains of single-pass transmembrane homophilic CAMs. We analyzed the structure and homophilic interactions of carcinoembryonic antigen (CEA)-related CAM(More)