Theory and modeling of stereoselective organic reactions

Theoretical investigations of the transition structures of additions and cycloadditions reveal details about the geometries of bond-forming processes that are not directly accessible by experiment. The conformational analysis of transition states has been developed from theoretical generalizations about the preferred angle of attack by reagents on multiple bonds and predictions of conformations with respect to partially formed bonds. Qualitative rules for the prediction of the stereochemistries of organic reactions have been devised, and semi-empirical computational models have also been developed to predict the stereoselectivities of reactions of large organic molecules, such as nucleophilic additions to carbonyls, electrophilic hydroborations and cycloadditions, and intramolecular radical additions and cycloadditions.

Transforming Sloan-Kettering viruses generated from the cloned v-ski oncogene by in vitro and in vivo recombinations

The Sloan-Kettering viruses (SKVs) are replication-defective retroviruses that transform avian cells in vitro. Each of the three SKV isolates is a mixture of viruses with genomes ranging in size from 4.1 to 8.9 kilobases (kb) with a predominant genome of 5.7 kb. Using a cDNA representing a sequence, v-ski, that is SKV specific and held in common by the multiple SKV genomes, we generated a restriction map of the 5.7-kb SKV genome and molecularly cloned a ski-containing fragment from SKV proviral DNA. Southern hybridization and sequence analysis showed that the cloned DNA fragment consisted of the 1.3-kb ski sequence embedded in the p19gag sequence and followed by the remaining 5' half of the gag gene and small portions of both the pol and env genes. A large deletion encompassing the 3' half of gag and the 5' 80% of pol was mapped to a position about 1 kb downstream from the 3' ski-gag junction. To determine whether the cloned ski sequence had transforming activity, the ski-containing fragment and a cloned Rous-associated virus 1 (RAV-1) genome were used to construct an analog of the 5.7-kb SKV genome, RAV-SKV. Cotransfection of chicken embryo cells with RAV-SKV and RAV-1 yielded foci of transformed cells whose morphology was identical to that induced by the natural SKVs. The transformed transfected cells produced transforming virus with a 5.7-kb ski-containing genome and synthesized a gag-containing polyprotein of 110 kilodaltons (kDa). Several nonproducer clones of RAV-SKV-transformed cells were analyzed, and most were found to synthesize a 5.7-kb SKV RNA and a 110-kDa polyprotein. One clone was found to contain an 8.9-kb SKV RNA, and this clone synthesized a 125-kDa polyprotein. Since both the 5.7- and 8.9-kb genomes and the 110- and 125-kDa polyproteins had been identified in studies on the natural SKVs, the present results not only demonstrate the transforming activity of these individual SKVs but also suggest mechanisms for their generation.

Unique sequence, ski, in Sloan-Kettering avian retroviruses with properties of a new cell-derived oncogene

The Sloan-Kettering viruses (SKVs) are a group of transforming retroviruses that were isolated from chicken embryo cells which had been infected with the avian leukosis virus transformation-defective Bratislava 77 (tdB77). Each of the SKV isolates was shown to contain multiple genomes of different sizes indicating the presence of several viruses in addition to tdB77. To identify and characterize the putative transforming gene(s) of the SKVs, we used hybridization selection to isolate the fraction of a representative cDNA which was SKV specific. Both solution and blot hybridization studies with viral RNAs showed that the specific probe contained a sequence, ski, that was at least partially held in common by the multiple SKV genomes. This conclusion was confirmed by the observation that a molecularly cloned ski probe also hybridized to each of the multiple SKV genomes. Southern blots of chicken DNA revealed homologs of ski (c-ski) which were not associated with endogenous viral loci. Results showing that c-ski was expressed in polyadenylated cytoplasmic RNA of uninfected chicken cells indicated that it is a functional gene. Other data showed that c-ski was conserved in avian and mammalian evolution, suggesting a functional role for the gene in species other than chickens. Using ski cDNA in solution hybridizations with viral RNAs and in Southern blot hybridization with cloned retroviral oncogenes, we did not detect any relationship between ski and any of 15 previously identified oncogenes.

Bovine interstitial retinol-binding protein (IRBP)--isolation and sequence analysis of cDNA clones, characterization and in vitro translation of mRNA

Three clones for b-IRBP were isolated by anti b-IRBP screening of two bovine retina libraries in the expression vector lambda gt11. The cDNA inserts were then used as hybridization probes to screen and isolate three more clones in a bovine retina library in the non-expression vector lambda gt10. The six overlapping clones generated a b-IRBP cDNA sequence of 3400 nucleotides. An open reading frame encoded the complete amino acid sequences of 8 of the 35 b-IRBP tryptic peptides purified in the present study. One tentative glycosylation site was identified. The coding region was followed by TAG translation terminating codon and an untranslated stretch of about 1700 nucleotides that ended in a sequence containing a presumptive AATAAA polyadenylation signal that was 18 nucleotides upstream from a 10 nucleotide oligo(A) tract. The coding region for b-IRBP would be expected to be 3300 bp long, but Northern blot hybridization experiments performed with bovine retina polyadenylated RNA and probes containing part of the coding region established that the mRNA for b-IRBP consisted of a major species of about 6300 bp, and a minor species of 5200 bp. In vitro translation of bovine retina polyadenylated RNA in a rabbit reticulocyte lysate system yielded an immunoreactive protein that was comparable in size with nonglycosylated, mature IRBP, showing that it is not synthesized from a large precursor, and supporting our finding that the mRNA contains an extensive non-coding region.

[Endocrine pancreatic tumor secreting somatostatin and somatocrinin]

A case of endocrine pancreatic tumour secreting the 2 antagonistic peptides that regulate growth hormone, somatostatin and somatocrinin, is reported. Such tumours are extremely rare and only one other case has been published so far, although pancreatic malignant tumours frequently secrete several hormones. In our patient, the association of diabetes with steatorrhoea, hypochlorhydria, anaemia and biliary lithiasis suggested hypersecretion of somatostatin. Acromegaly, suggested by clinical signs, was confirmed by an excess of growth hormone and somatomedin, and pre-operative somatrocrinin assay confirmed its extra-pituitary origin. Finally, the presence of hyperparathyroidism due to parathyroid gland hyperplasia and of a Recklinghausen disease constituted a multiple endocrine neoplasia syndrome. The significance and implications of this double secretion in vivo are discussed.

Effect of filler content and size on properties of composites

Two series of dental composites, along with the unfilled resin matrix, were examined to determine the effects of filler level and size on selected properties. Both series were prepared by incorporating a silanated barium borosilicate filler into a visible-light-activated polyphenylene polymethacrylate resin matrix. One series had a filler particle size of 2 microns, with filler levels of 20, 40, 45, 50, and 53% (vol). The second series contained a 15-microns filler in amounts of 20, 40, 50, 60, and 65% (vol). Tests conducted included: depth of cure as evaluated by hardness, water sorption, compressive strength, stress-strain behavior under slow compression, toothbrush abrasion, and wear by hydroxyapatite. Analysis of the data indicated that increased filler levels resulted in increased hardness, compressive strength and stiffness, and decreased water sorption. Also, there was a slight trend toward improved depth of cure. Incorporation of the 2-microns filler decreased the abrasion resistance of the resins to toothbrushing as compared with the unfilled resin, while addition of the 15-microns filler improved resistance. All filled resins exhibited a significant improvement in resistance to wear by hydroxyapatite as compared with the unfilled resin. There was a trend for increased wear with increased filler level. The particle size of the filler appeared to have a moderate influence on the properties. When compared with 15-microns filled resins of the same filler levels, the 2-micron filled series appeared to have inferior properties in terms of depth of cure, compressive strength, water sorption, and resistance to toothbrush abrasion. Properties which were less affected by particle size were hardness, stiffness, and wear resistance to hydroxyapatite.

Oroclinal Bending of the Southern Sierra Nevada Batholith

Structural, magmatic, and isotopic features of the southern Sierra Nevada batholith are deflected clockwise with respect to its central and northern parts. Directions of magnetization at three localities in the southern Sierra Nevada are progressively deflected; this is consistent with the hypothesis that the region was tectonically rotated in an orocline. No paleomagnetic deflection was observed northwest of the White Wolf-Kern Canyon fault system. Oroclinal bending ofa block bounded by the San Andreas, Garlock, and White Wolf-Kern Canyon faults may have occurred before about 16 x l0(6) years ago. The deformation may have been a response to shear at the western boundary of the North American plate caused by oblique subduction.

Chicken heart ubiquinol: cytochrome c reductase--isolation by affinity chromatography and resolution of enzyme into subunits

Chicken heart mitochondrial ubiquinol: cytochrome c reductase has been isolated as a monodisperse form by solubilization with Triton X-100 in low ionic strength and subsequent affinity chromatography. The enzyme complex contains less than 0.15 mumol ubiquinone and 12 mumol phospholipid per mumol enzyme. The spectrum of cytochrome b in the reduced exhibited two maximum alpha-absorption bands at 558 nm and 562 nm; a shoulder at 553 nm for c1. The purified enzyme complex consists of at least 9 subunits with apparent molecular weight of 47 K, 44 K, 36 K, 31 K, 25 K, 17 K, 15 K, 12 K and 9 K. The enzyme complex has been dissociated into subdomains of subunits in the presence of increasing concentration of salt and Triton X-100. Three subunits carrying the redox centers (cytochrome b, cytochrome c1 and Fe-S protein) have been further isolated.