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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)
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)
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)
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)
The growth and maturation of the transcription products on the Balbiani ring (BR) genes in Chironomus tentans has been characterized by electron microscopy. The BR transcript is packed into a series of well defined ribonucleoprotein structures of increasing complexity: a 10 nm fiber, a 19 nm fiber, a 26 nm fiber, and a 50 nm granule. The basic 10 nm element(More)
Structures in situ of individual ribosomes in E. coli have been determined by computer-aided electron microscope tomography using a tilt series of positively stained embedded cellular sections. Amino acid starvation of a bacterial culture, causing a deficiency for aminoacyl-tRNA, induces a spatial separation between the ribosomal subunits compared with(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)
Filtered back-projection and weighted back-projection have long been the methods of choice within the electron microscopy community for reconstructing the structure of macromolecular assemblies from electron tomography data. Here, we describe electron lambda-tomography, a reconstruction method that enjoys the benefits of the above mentioned methods, namely(More)
Caveolin plays an essential role in the formation of characteristic surface pits, caveolae, which cover the surface of many animal cells. The fundamental principles of caveola formation are only slowly emerging. Here we show that caveolin expression in a prokaryotic host lacking any intracellular membrane system drives the formation of cytoplasmic vesicles(More)