Serial section reconstruction using a computer graphics system: Applications to intracellular structures in yeast cells and to the periodontal structure of dogs' teeth

A computer graphics system for reconstruction from serial section micrographs was applied to intracellular details of a yeast target cell (Saccharomyces cerevisiae cell) induced by the α factor mating pheromone and was also applied to a periodontal structure of a dog tooth moved orthodontically. In the former, intracellular organelles and a distribution of vesicles could be clearly observed through the cell membrane using the transparent display method in which the smoothing of the reconstructed outer cell membrane surface by computer processing was applied to the transparent display. In the latter case, by cutting through a reconstructed dog tooth and its periodontal tissues, labiolingual and mesiodistal cut surfaces of the tooth and of adjacent alveolar bone could be observed with fine details (232 sections were used).     

Isolation and characterization of long-chain-alkane degrading Bacillus thermoleovorans from deep subterranean petroleum reservoirs

Two extremely thermophilic alkane-degrading bacterial strains, B23 and H41, were respectively isolated from deep subterranean petroleum reservoirs in the Minami-aga (Niigata) and Yabase (Akita) oil fields. Both strains were able to grow at temperatures ranging from 50 to 80 degrees C, with optimal growth at 70 degrees C for B23 and 65 degrees C for H41. From 16S rRNA gene sequence analysis and physiological characterization, both strains were identified as Bacillus thermoleovorans (identities of 99.5% and 99.6% to strain DSM 5366, and 98.3% and 98.7% to the type strain LEH-1(TS), respectively). Strains B23 and H41 effectively (60%) degraded n-alkanes longer than C12 and C15, respectively, at 70 degrees C, while strain LEH-1(TS) degraded undecane (C11) most effectively. When B23 and H41 were cultivated in the presence of heptadecane, heptadecanoate and pentadecanoate were specifically accumulated in the cells. These results strongly suggest that the two strains degraded n-alkanes by a terminal oxidation pathway, followed by a beta-oxidation pathway.     

The conversion of a field-emission scanning electron microscope to a high-resolution,high-performance scanning transmission electron microscope,while maintaining original functions

Recently, the reliability of field-emission electron guns has increased. In addition, the cost of computer systems for on-line processing has dropped. Hence, we should now consider the use of scanning transmission electron microscopy (STEM) for routine work, especially, in the field of biology where one may expect to utilize digital image processing techniques. An STEM has been constructed, without disturbing the original functions, by converting a commercial scanning electron microscope equipped with a fieldemission gun. The STEM is generally operated at accelerating voltage 30 kV, focal length 7.5 mm, and beam current 1?2 × 10^?10 A. Several improvements have been incorporated for removing the effects of vibration, contamination, and stray magnetic fields. Also, an adjustable detector aperture was utilized. The modified instrument was connected to an on-line digital image processing system for utilizing the information obtained from STEM images. The advantages of the modified system were studied from various viewpoints.     

Simultaneous SAXS/WAXS experiments on shear induced iPP crystallization near nominal melting temperature

Simultaneous small- and wide-angle synchrotron radiation X-ray scattering was performed to monitor the evolution of crystalline structure within the iPP melt during and after applying pulse shear. The iPP melt was subjected to a strong pulse shear of 240 s^?1 for 6 s at temperatures between 150 and 170 °C below and above the nominal melting temperature T_m. It was found that the imposed shear affected the melt only at lowest temperature. Structures generated during flow above 150 °C were too dilute to be detected. To extract the hidden structure, the melt was cooled to crystallization temperature of 150 °C either immediately after shearing or after annealing at shear temperature for up to 30 min. This treatment manifested with an anisotropic structure in a few minutes after quenching, undetectable when both shear and annealing temperatures presented the same value. The data obtained revealed also close correlations between annealing time, shear temperature and incubation time.     

Brain potentials associated with eye fixations during visual tasks under different lighting systems

The incidence of non-familial multiple primary cancer in colorectal cancer patients has increased in recent years in Japan. To clarify the characteristic genetic aberrations in such multiple cancers, we examined structural chromosomal aberrations by fluorescence in situ hybridization, using chromosome 17-specific and p53 cosmid DNA probes. We established short-term cultures of 78 surgical specimens and were able to obtain observable metaphase spreads in 23 single colorectal cancer specimens and in 6 colorectal cancer specimens from patients with double primary cancers. The frequency of chromosome 17 and/or p53 locus translocation was significantly greater in tumors with double cancer than in single colorectal cancers (P < 0.05 and P < 0.01, respectively). These aberrations in double cancers frequently appeared even at an early Dukes' stage (A and B) of colorectal carcinoma. Our results suggest that translocation of chromosome 17 and the p53 locus may be specific genetic events probably associated with carcinogenesis of multiple primary cancers in colorectal cancer.     

Gene cloning and characterization of recombinant RNase HII from a hyperthermophilic archaeon

We have cloned the gene encoding RNase HII (RNase HIIPk) from the hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1 by screening of a library for clones that suppressed the temperature-sensitive growth phenotype of an rnh mutant strain of Escherichia coli. This gene was expressed in an rnh mutant strain of E. coli, the recombinant enzyme was purified, and its biochemical properties were compared with those of E. coli RNases HI and HII. RNase HIIPk is composed of 228 amino acid residues (molecular weight, 25,799) and acts as a monomer. Its amino acid sequence showed little similarity to those of enzymes that are members of the RNase HI family of proteins but showed 40, 31, and 25% identities to those of Methanococcus jannaschii, Saccharomyces cerevisiae, and E. coli RNase HII proteins, respectively. The enzymatic activity was determined at 30 degreesC and pH 8.0 by use of an M13 DNA-RNA hybrid as a substrate. Under these conditions, the most preferred metal ions were Co2+ for RNase HIIPk, Mn2+ for E. coli RNase HII, and Mg2+ for E. coli RNase HI. The specific activity of RNase HIIPk determined in the presence of the most preferred metal ion was 6. 8-fold higher than that of E. coli RNase HII and 4.5-fold lower than that of E. coli RNase HI. Like E. coli RNase HI, RNase HIIPk and E. coli RNase HII cleave the RNA strand of an RNA-DNA hybrid endonucleolytically at the P-O3' bond. In addition, these enzymes cleave oligomeric substrates in a similar manner. These results suggest that RNase HIIPk and E. coli RNases HI and HII are structurally and functionally related to one another.     

Surface adsorption of propane, propylene and propane/propylene mixed gas on polyimide observed with X-ray and neutron reflectivity

We observed the surface adsorption layer of propylene, propane and propane/propylene mixed gas on a polyimide film as a function of pressure using X-ray (XR) and neutron (NR) reflectivity. It was initially confirmed by NR that the surface layer is an adsorption layer of propylene using deuterated gas. We have determined by XR the adsorption isotherms of these gases and found that the thickness of the surface adsorption layer of propane and propane/propylene mixed gas is much larger than that of propylene and the isotherm of propane/propylene mixed gas is similar to that of propane. The former and the latter findings predict that the affinity of propane to the polyimide is greater than propylene and the content of propane is much higher than that of propylene in the adsorption layer. We also evaluated the permeability coefficients of these gases as a function of the applied pressure, and found that the permeability coefficients begin to increase at a pressure corresponding to the onset of the adsorption layer. This suggests that the surface adsorption layer of the gas plays an important role in the hydrocarbon gas permeation mechanism in a polymer membrane, while a swelling of the polyimide film is the basis for the increase in the permeability with pressure.     

Relationship between the local dynamics and gas permeability of polyacetylenes containing polymethylated indan/tetrahydronaphtalene moieties

Local dynamics of polyacetylenes having polymethylated indan/tetrahydronaphthalene moieties have been studied using quasielastic neutron scattering, and the results obtained have been discussed together with former results with various poly(diphenylacetylene) derivatives. Clear quasielastic scattering was observed for the present polymers although they were in the glassy state, and the observed dynamic scattering laws were well fitted to a model function assuming the sum of narrow and broad Lorentzians. Both the relaxation rates and fractions from the narrow component exhibited a positive correlation with oxygen permeability coefficients (PO₂)$\left(P_{{\text{O}}_2}\right)$, while those from the broad component hardly related to PO₂$P_{{\text{O}}_2}$. Furthermore, the local flux, which is defined as the product of fraction and relaxation rate of the narrow component, is also found to be proportional to PO₂$P_{{\text{O}}_2}$. These findings imply that only the narrow component contributed to the gas permeability. Thus, it has been clarified that the local dynamics with a time scale of several tens of picoseconds plays a role of key importance for the gas permeability of substituted polyacetylenes in the glassy state.     

Annealing effects on thickness of polystyrene thin films as studied by neutron reflectivity

We performed neutron reflectivity measurements on deuterated polystyrene thin films supported on silicon substrate as a function of temperature. In order to see effects of annealing on the thickness, the films were annealed at 80 °C for 12 h and 135 °C for 12 h, termed weakly and strongly annealed films, respectively. One of the main purpose of this study is to see if the negative expansivity reported for very thin films [Phys. Rev. Lett. 71 (1993) 867] is caused by unrelaxed structure due to lack of annealing. It was found that the weakly annealed films show negative expansivity in the glassy state and it disappears for the strongly annealed films with thickness above about 90 Å. This suggests that the negative expansivity is due to the unrelaxed structure. In addition to this relaxation process, the thickness difference between the heating process and the cooling process suggests that there is another very slow relaxation process in thin films detectable at around 135 °C or about 32 °C above the glass transition temperature T_g. As a candidate for this slow process a sliding motion proposed by de Gennes is discussed.