Effect of cellular level of FliK on flagellar hook and filament assembly in Salmonella typhimurium

Frameshift mutations in the fliK gene of Salmonella result in abnormal elongation of the hook and the failure to assemble filament (polyhook phenotype). Second-site suppressor mutations restore filament assembly, but the cells often remain defective in hook-length control (polyhook-filament phenotype). Where the suppressor mutations are intragenic, the second mutation restores the original frame, generating a region of frameshifted sequence, but restoring the natural C terminus. Some of these frameshifted sequences contain a UGA (opal) termination codon. These cells have few flagella and swarm poorly. We suspected that readthrough of UGA by tRNATrp might be the reason for the partial function. When the UGA codon was changed to the Trp codon UGG, flagellar assembly and function were restored to wild-type levels. Conversely, underexpression of the wild-type fliK gene, achieved by changing the sole Trp codon in the sequence (Trp271) to UGA, decreased both the number of flagella and the ability to swarm. These results validate the readthrough hypothesis and indicate that low levels of FliK sustain some degree of flagellation and motility. At low levels of FliK, most flagella had polyhooks. With increasing amounts, the morphology progressively changed to polyhook-filament, and eventually to wild-type hook-filament. When FliK was overproduced, the hook length was slightly shorter (46(+/-7) nm) than that of the wild-type strain (55(+/-9) nm). FliK levels were measured by immunoblotting. Wild-type levels were about 40 to 80 molecules/cell. FliK synthesized by UGA readthrough could be detected when overproduced from plasmid fliK-W271opal, and the levels indicated a probability of readthrough of 0.002 to 0.01. This value was used to estimate the cellular level of underexpressed FliK, which could partly restore function to a fliK mutant, at about 0.07 to 0.8 molecule/cell. These results suggest that FliK does not form a large structure in the cytoplasm and may function as a regulatory protein for protein export. A model for hook-length control is presented that involves feedback from the assembly point to the export apparatus.     

Site-Dependent Study of the Optical Properties of Eu3+ in Pure and Chlorine-Doped Fluorozirconate Glasses

For the present study, the emission spectra and lifetimes of Eu³⁺ in fluorozirconate and fluorochlorozirconate glasses were measured site dependently using the fluorescence line narrowing (FLN) technique. At high excitation energies, two different types of Eu³⁺ sites can be distinguished in fluorozirconate glass. The introduction of chloride into this glass caused a significant effect at low excitation energy.     

Yellow Coatings Produced on Glasses and Aluminum by the Sol-Gel Process

The preparation of CeO₂-TiO₂ coatings by the sol-gel dip-coating process, with curing at 500°C, was studied. The films were brilliant yellow and adherent to soda-lime glass, a PbO-containing glass, and aluminum foil. The transmittance, chromaticity, thickness, phase content, and surface microstructure of the films were determined.     

A Machinable Calcia–Alumina–Yttria–Silica Glass-Ceramic

It is found that a crystallized aluminosilicate glass having needlelike Ca₄Y₆O(SiO₄)₆ crystals is machinable. Densities, Vickers hardnesses, Young's moduli, thermal expansion coefficients, and fracture toughnesses of the crystallized glasses were measured.     

Greater synergism of retinoic acid receptor (RAR) agonists with vitamin D3 than that of retinoid X receptor (RXR) agonists with regard to growth inhibition and differentiation induction in monoblastic leukemia cells

Retinoids and 1alpha,25-dihydroxyvitamin D3 (VD3) cooperatively induce the differentiation of myeloid leukemia cells. We investigated the role of retinoid receptors (RARs and RXRs) in the combined effects of retinoids and VD3 on growth inhibition and differentiation induction in human monoblastic leukemia U937 cells by using RAR- or RXR-selective retinoids. An isobologram analysis showed that both combinations were synergistic with regard to inhibiting the proliferation, and RAR agonists exhibited greater synergism with VD3 than did RXR agonists. RXR agonists alone induced nitroblue tetrazolium (NBT) reduction and expression of CD11b in U937 cells, whereas RAR agonists alone did not. On the other hand, RAR agonists and RXR agonists enhanced the differentiation induced by VD3, but RXR agonists required higher concentrations. An RAR antagonist inhibited the differentiation induced by RAR agonists plus VD3, but not that induced by RXR agonists plus VD3. Thus, RARs and RXRs act differently in their synergism with VD3. RAR agonists are more potent than RXR agonists with regard to synergism with VD3, and their combination may be useful in differentiation therapy against myeloid leukemia.     

Speech audiometry using the American Word Lists for Japanese subjects with normal hearing

The characteristics of listening to English words for Japanese people were studied in ten normal hearing subjects who had taken English classes to the level of college graduates and had opportunities to learn English continuously. Following pure tone audiometry, speech audiometry was performed using the Central Institute for the Deaf (CID) W-1 and W-22 word lists for English and the 67-S word lists for Japanese. The speech reception thresholds (SRTs) for the CID W-1 lists were significantly higher than average pure tone threshold (PTT), although the SRTs for the 67-S lists were equal to the average PTT. The difference in average SRT between the CID W-1 lists and the 67-S lists was about 15dB, which is statistically significant. The speech discrimination rate for the CID W-22 lists ranged from 78 to 100 percent with an average of 89.5 percent, while all subjects achieved the discrimination rate of 100 percent for the 67-S lists. Analysis with transient matrices of the perceived words demonstrated that the articulation rates were below 90 percent for the consonants /m/, /n/, /p/ and /delta/ . The observed variation in the speech discrimination score and the pattern of confusion among the subjects was assumed to be much more pronounced in noisy conditions.     

Positronium Annihilation Study of Porosity in Silica Xerogels Prepared by a Sol–Gel Process

Nano- and mesopores of bulk silica xerogels were studied by means of positron annihilation lifetime measurement as well as nitrogen physisorption. Effects of an alkaline catalyst concentration in the sol–gel process on the pore sizes and specific surface area were investigated. The pore size was estimated from the ortho -positronium lifetime. Remarkable structural changes were found around a relative alkaline concentration of 10⁻⁴ (a molar ratio of sodium hydroxide to tetramethyl ortho -silicate). Above this particular catalyst concentration, the nanopore radius decreased from 0.45 to 0.35 nm, whereas the mesopore radius increased from 1 to 8 nm. The positron annihilation lifetime technique was effective in the evaluation of the nano- and mesoscopic structural changes of silica xerogel.     

A group separation method for ruthenium, palladium, rhenium, osmium, iridium, and platinum using their bromo complexes and an anion exchange resin.

A new group separation method for Re and PGE (Ru, Pd, Os, Ir, Pt) is described using a novel anion exchange chromatographic resin called TEVA. Re and PGEs are converted into bromo complexes by heating with HF-HBr mixture in a Teflon bomb at 518 K, by in situ-generated Br2 formed by reaction of HBr and HNO3. Distribution coefficients (Kd) of the bromo complexes onto TEVA resin in 0.1 M HBr with heating at 353 K for one night were 2,200, 16,000, 1,600, 5,500, 4,000, and 17,000 for Ru, Pd, Re, Os, Ir, and Pt, respectively, thus allowing 97% recovery of Re and PGEs in 5 mL of solution by 0.1 mL of resin. These strongly bound Re and PGE bromo complexes are stripped and recovered >90% by the following three steps: (i) addition of 6 M HCl at 353 K and 2.2 M HCl-5 M HBr at 353 K; (ii) heating the resin in 6 M HCl at 353 K to convert the bromo complexes into the chloro complexes with weaker affinities to the resin; and (iii) sequential addition of the HCl-HBr mixture at room temperature and 7 M HI. Neither the elution profile nor the recovery yield for a 0.2-g geological sample showed significant changes, indicating minimal matrix effects for the geological samples. Total blanks were < 14 pg for Ru, Pd, and Pt and < 10 pg for Re, Os, and Ir. This new technique, therefore, is suitable for simultaneous determination of subnanogram per gram of Ru, Pd, Re, Os, Ir, and Pt and Os isotope analysis in geological, mineralogical, and environmental samples without direct addition of toxic reagents required in distillation/extraction of Os or oxidizing of Ir.