Search PubMed⌕ Search

Biomedical subjects

U Skoglund

Publications and source records attributed to U Skoglund.

27 records · Page 2Linked to original sources
PubMed1991

Transport of Balbiani ring granules through nuclear pores in Chironomus tentans.

Balbiani ring granules are premessenger RNP particles synthesized in the larval salivary glands of the dipteran Chironomus tentans and containing the genetic information for large-sized secretory proteins. The granules in the nucleoplasm consist of a thin elementary RNP fiber tightly packed into an RNP ribbon, which is bent into a ring-like shape. When the 50-nm granule is translocated through the nuclear pore, it attains an elongated conformation. We have now demonstrated that the particle in transition can be described as an RNP ribbon with the same thickness and the same minimal width as the ribbon of the nucleoplasmic granules. The ribbon in the pore is, however, somewhat longer and it lacks the broad regions of the ribbon in the nucleoplasmic granule. We conclude that when entering the pore the bent ribbon of the Balbiani ring granule is being straightened and also somewhat drawn out, while its width is accommodated to the maximal size of the pore, i.e., about 25 nm. On the cytoplasmic side the ribbon is unpacked, and the elementary fiber can be seen extending into cytoplasm, probably being available for polysome assembly.

Animals↗
PubMed1990

Isolation and initial characterization of a specific premessenger ribonucleoprotein particle.

A specific type of premessenger ribonucleoprotein (RNP) particle, Balbiani ring (BR) granules, has been isolated from heterogeneous nuclear RNP (hnRNP) in the salivary glands of the dipteran Chironomus tentans. A BR granule contains a single 75S RNA molecule coding for a large secretory protein (Sp1). The isolation procedure is based on the abundance and exceptional size of the BR granules: in EDTA-containing sucrose gradients they sediment as a sharp 300S peak ahead of the remainder of the hnRNP population. The isolated BR granules were identified on the basis of both ultrastructural and biochemical criteria: large spherical particles that contain 75S RNA and BR sequences. A three-dimensional reconstruction of isolated particles by electron microscope tomography further supported the identification of the isolated particles as BR granules. In contrast to the entire hnRNP population, the BR granules exhibited a sharp peak in CsCl gradients with a buoyant density of 1.45 g/cm3. This result indicates that a BR granule consists of 40% RNA and 60% protein by weight, corresponding to a 75S RNA molecule of 12 megadaltons and a total protein content of 18 megadaltons, or about 500 average-sized protein molecules.

Animals↗
PubMed1987

Structure of RNA in satellite tobacco necrosis virus. A low resolution neutron diffraction study using 1H2O/2H2O solvent contrast variation.

The crystal structure of satellite tobacco necrosis virus has been studied by neutron diffraction at 16 A resolution using the technique of 1H2O/2H2O solvent contrast variation to distinguish between the regions of protein and nucleic acid. The RNA density is essentially localized in a region just inside the protein coat, leading to a significant interaction between the two components. From the appearance of the RNA density we conclude that the protein coat imposes partial icosahedral symmetry on a significant proportion of the nucleic acid. The shape and dimensions of the major part of this density suggests that about 72% of the total RNA could be double-helical in structure. The most important interaction between the two components of the virus occurs between the N-terminal triple-helical arms of the protein subunits and those regions of the RNA density that could have a double-helical secondary structure.

Amino Acid Sequence↗
PubMed1983

Visualization of the formation and transport of a specific hnRNP particle.

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 was revealed in Miller spreads. The in situ structure of the transcription products and RNA compaction estimates suggested that the 10 nm fiber is packed into the 19 nm fiber as a tight coil. The transition of the 19 nm fiber into the 26 nm fiber is accompanied by a major change of the basic 10 nm fold into a noncoiled structure. Finally, the 26 nm fiber makes a one and one-third left-handed turn forming the final product, the BR granule. Upon translocation through the nuclear pore the BR granule becomes rod-shaped, which most likely corresponds to a relaxation of the highest-order structure into a straight 26 nm fiber.

Animals↗
PubMedDate not supplied

Maximum-entropy three-dimensional reconstruction with deconvolution of the contrast transfer function: a test application with adenovirus.

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 produce the most featureless reconstruction that fits the projection data within their observational accuracy. In particular, the COMET procedure will minimise the detrimental effects of errors in the measured data and deconvolute the effects of the contrast transfer function. An objective test has been performed using COMET on a conventional image reconstruction obtained from cryo-electron micrographs of adenovirus. The density for hexon, the major coat protein of the virus, which is known to high resolution from X-ray crystallography, provided a known high-resolution control. The COMET reconstruction is in considerably better agreement with the crystallographic electron density than the original reconstruction, throughout the entire resolution range.

Adenoviridae↗
PubMedDate not supplied

Three-dimensional structure of a specific pre-messenger RNP particle established by electron microscope tomography.

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 of the transcript, and the fourth domain, containing the 3' end, are close to each other.

Animals↗