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R H Vogel

Publications and source records attributed to R H Vogel.

10 recordsLinked to original sources
PubMed1988

Three-dimensional reconstruction from electron micrographs of disordered specimens. I. Method.

A method is presented for three-dimensional reconstruction from electron micrographs of a specimen containing a disordered collection of identical objects with unknown orientations. All the data from all the images are simultaneously used to obtain an approximately maximum likelihood estimate of the three-dimensional electron density, which is represented as a truncated expansion in a complete orthonormal set of basis functions. Anomalous objects can nevertheless be detected and eliminated. The method remains under statistical control, and a hypothesis test is used to choose the lowest resolution reconstruction that is consistent with the data. Error propagation is quantitatively traced from the micrograph to the reconstructed electron density. Random orientation is not necessary, and prior knowledge of preferred orientation can be used to advantage. Similarly, symmetry in the object is not necessary, but it can be imposed and exploited, if appropriate. Evidence is presented that useful reconstructions can be obtained with only one or two extra tilts from highly disordered specimens, even if the objects are asymmetric. The companion paper discusses in detail the implementation and verification of the method.

Mathematics↗
PubMed1988

Three-dimensional reconstruction from electron micrographs of disordered specimens. II. Implementation and results.

The computational procedures to implement the method described in the companion paper for three-dimensional reconstruction from projections of a disordered collection of single particles are presented. Computer simulations are used to demonstrate the way the method functions, and practical aspects are discussed in detail. Examples are given of how different symmetries can be exploited by imposing selection rules on the model equations. Applications to negatively stained 50S ribosomes and to cryo-electron micrographs of thin vitrified layers of unstained and unsupported tomato bushy stunt and Semliki Forest viruses are described, and the resulting reconstructions are presented.

Geobacillus stearothermophilus↗
PubMed1983

Binding of phorbol dibutyrate and epidermal growth factor to cultured human epidermal cells.

Primary cell cultures of normal human epidermal keratinocytes and melanocytes and human cell lines established from a primary melanoma (SK-PM-4) and metastatic melanomas (HO#1, SK-MEL21, and SK-MEL37) contain specific and saturable receptors for the tumor promoter phorbol dibutyrate (PDBu). Scatchard analyses of the keratinocytes revealed two classes of binding sites: 1) a high-affinity class (affinity constant = 37 nM; 1.3 X 10(6) sites/cell) and a low-affinity class (affinity constant = 4,880 nM; 7 X 10(7) sites/cell). The melanoma cultures, likewise, showed high- and low-affinity classes of PDBu binding sites. However, the affinity constant values and total numbers of sites in the melanoma cells were lower than the corresponding values in the keratinocytes. The binding of [3H]PDBu to human keratinocytes was inhibited by the tumor promoters 12-O-tetradecanoylphorbol 13-acetate and teleocidin but not by phorbol, which lacks tumor-promoting activity. Human serum also inhibited binding. Specific receptors for epidermal growth factor (EGF) were demonstrated in the keratinocytes and primary melanoma cultures. In contrast, three metastatic melanoma cultures gave negligible levels of EGF binding. Among the various cell types, the extent of [3H]PDBu binding did not correlate with the extent of EGF binding, indicating that these two substances occupy distinctly separate types of receptors.

Caenorhabditis elegans Proteins↗
PubMed1979

Clustered arg genes on a BamHI segment of the Escherichia coli chromosome.

BamHI cleavage of DNAs from transducing phages gamma darg13 (ppc, argECBH, bfe), gamma darg14 (ppc, argECBH) and gamma darg23 (argECBH) yields three purely gamma DNA segments (and, in one case, a fourth), as well as several Excherichia coli-DNA-containing segments. The length (in kilobases, kb) of the segments, determined by electron microscopy and ararose gel electrophoresis is 4.2, 7.5, 8.4, 6.2, 6.9, and 6.4 kb for gamma darg13; 13.0, 7.5, 4.7, 6.2, 6.9, and 6.4 kb for gamma darg 14: and 5.3, 11.0, 4.7, 6.2, 6.9, and 6.4 kb for gamma darg23. Ordering of the segments (in relation to the gamma genetic map and with the direction from left to right corresponding to the clockwise orientation of the E. coli genetic map and to each of the numerical sequences given) reveals, on 26 kb of bacterial DNA, two cleavage sites defining the 7.5-kb segment obtainable from the DNA of either gamam darg13 or gamma darg14. These and analogous findings with argEC and argCB deletion-bearing strains, together with results from heteroduplex experiments, locate argE, argC, argB, and presumably argH on the 7.5-kb segment.

Arginine↗
PubMed1978

Evidence for translational repression of arginine biosynthetic enzymes in Escherichia coli: altered regulation in a streptomycin-resistant mutant.

The formation and repressibility of the arginine biosyntietic enzymes acetylornithine delta-aminotransferase (EC 2.6.1.11), acetylornithine deacetylase (EC 3.5.1.16), ornithine carbamoyltransferase (EC 2.1.3.3), and argininosuccinate lyase (EC 4.3.2.1) were studied in an Escherichia coli W derivative (strain 250-10) that carries (a) a mutant allele of the argR regulatory gene causing a diminished repression-derepression range and (b) a streptomycin resistance mutation. In comparison with the streptomycin-sensitive parent 250, all four enzymes (a) are formed as smaller proportions of the total protein (overall range, 12% to 71%), whether the conditions are repressive (arginine excess) or derepressive (arginine restriction), and (b) show increased repressibility ratios, the carbamoyltransferase giving the largest increase (from 5.7 to 25.0). These effects appear to depend on the concurrent expression of the regulatory-gene and streptomycin resistance mutations, as indicated by analogous experiments with canavanine-resistant mutants of 250-10 that have partial argR- character. The results provide evidence for translational repression in the arginine system, and are interpreted in terms of a functional interaction of a mutant arginine repressor with a mutant S12 ribosomal protein. The locale of translational repression may be near the site of S12, and this mode of regulation may involve initiational selectivity of groupwise recognizable arginine messenger RNA's.

Acetamides↗
PubMed1978

Conflicts, trade-offs, and preference measurement.

The usefulness of preference measurement is extended by two techniques: the use of collapsed orthogonal arrays of factor combinations to reduce respondent time needed to indicate preferences among many factors and the use of monotonic analysis of variance to establish utility scales for individuals as well as for the group. Only main effects can be measured, but comparison of individual utility scales can aid the decision maker in gaining acceptance of decisions from group members whose preferences are not widely shared by the group. Use of these techniques is illustrated in a situation in which a few vocal members of a hospital medical staff were pressing the administrator for major changes in diagnostic facilities for out-patients.

Analysis of Variance↗
PubMed1969

Repression-dependent alteration of an arginine enzyme in Escherichia coli.

Treatment of susceptible Escherichia coli K12 derivatives with 0.4 M Mg(++) at 37 degrees , potentiated by L-arginine or L-canavanine, leads to alteration of acetylornithine delta-transaminase. The alteration, obtained in the absence of protein synthesis and reversible at 0 or 37 degrees , is manifested in extracts by lowered activity and modified substrate affinity behavior of the enzyme without gross changes in sedimentation properties. Cells grown under arginine repression are susceptible to the treatment; cells grown under genetic or steady-state physiological derepression are not. Transaminase synthesized during early derepression can be altered, although to progressively diminishing extents. Enzyme formed under steady-state derepression becomes alterable following transition to repression. The Mg(++) -dependent alteration can be thought to arise while the enzyme, arginine (or canavanine), and aporepressor are in contact, and to reflect a physiological process such as the participation of the enzyme in the repressive complex.

Arginine↗
PubMedDate not supplied

Envelope structure of Semliki Forest virus reconstructed from cryo-electron micrographs.

The basic principles of the architecture of many viral protein shells have been successfully established from electron microscopy and X-ray data, but enveloped viruses have been more difficult to study because they resist crystallization and are easily deformed when prepared for electron microscopy. To avoid the limitations of conventional techniques when applied to enveloped viruses, we have used a cryo-electron microscopy method in which unfixed and unstained viruses are observed in an unsupported thin layer of vitrified suspension. Because of electron beam damage, the many different views required for high-resolution three-dimensional reconstruction cannot be obtained from a tilt series of the same particle. The images of many differently oriented viruses are combined using a novel reconstruction method, 'reconstruction by optimized series expansion' (ROSE). The structure of the envelope of Semliki Forest virus has been reconstructed to 3.5-nm resolution. The T = 4 geometry of the surface lattice, the shape of the trimeric spikes and their arrangement on the lipid bilayer are visualized.

Freezing↗