Electron microscopic visualization of tRNA genes with ferritin-avidin: biotin labels

A method is described for indirect electron microscopic visualization and mapping of tRNA and other short transcripts hybridized to DNA. This method depends upon the attachment of the electron-dense protein ferritin to the RNA, the binding being mediated by the remarkably strong association of the egg white protein avidin with biotin. Biotin is covalently attached to the 3' end of tRNA using an NH2 (CH2) 5NH2 bridge. The tRNA-biotin adduct is hybridized to complementcrry DNA sequences present in a single stranded nonhomology loop of a DNA:DNA heteroduplex. Avidin, covalently crosslinked to ferritin is mixed with the heteroduplex and becomes bound to the hybridized tRNA-biotin. Observation of the DNA:RNA-biotin:avidin-ferritin complex by electron microsdopy specifically and accurately reveals the position of the tRNA gene, with a frequency of labeling of approximately 50%

Structure and spacing of cellulose microfibrils in woody cell walls of dicots

The structure of cellulose microfibrils in situ in wood from the dicotyledonous (hardwood) species cherry and birch, and the vascular tissue from sunflower stems, was examined by wide-angle X-ray and neutron scattering (WAXS and WANS) and small-angle neutron scattering (SANS). Deuteration of accessible cellulose chains followed by WANS showed that these chains were packed at similar spacings to crystalline cellulose, consistent with their inclusion in the microfibril dimensions and with a location at the surface of the microfibrils. Using the Scherrer equation and correcting for considerable lateral disorder, the microfibril dimensions of cherry, birch and sunflower microfibrils perpendicular to the [200] crystal plane were estimated as 3.0, 3.4 and 3.3 nm respectively. The lateral dimensions in other directions were more difficult to correct for disorder but appeared to be 3 nm or less. However for cherry and sunflower, the microfibril spacing estimated by SANS was about 4 nm and was insensitive to the presence of moisture. If the microfibril width was 3 nm as estimated by WAXS, the SANS spacing suggests that a non-cellulosic polymer segment might in places separate the aggregated cellulose microfibrils

Hemicellulose binding and the spacing of cellulose microfibrils in spruce wood

Cellulose microfibrils in conifers, as in other woody materials, are aggregated into loose bundles called macrofibrils. The centre-to-centre spacing of the microfibrils within these macrofibrils can be estimated from the position of a broad diffraction peak in small-angle neutron scattering (SANS) after deuteration. A known spacing of 3.0 nm, increasing with moisture content, is consistent with direct microfibril to microfibril contact. However recent evidence indicates that conifer microfibrils are partially coated with bound xylan chains, and possibly with lignin and galactoglucomannan, implying a wider centre-to-centre spacing as found in angiosperm wood. Delignification of spruce wood allowed a weak SANS peak to be observed without measurable change in spacing. By deuterating spruce wood in mildly alkaline D2O and then re-equilibrating with ambient H2O, deuterium atoms were trapped in a position that gave a 3.8 nm microfibril spacing under dry conditions as in angiosperm wood, instead of the 3.0 nm spacing normally observed in conifers. After conventional vapour deuteration of spruce wood a minor peak at 3.8 nm could be fitted in addition to the 3.0 nm peak. These observations are consistent with some microfibril segments being separated by bound xylan chains as in angiosperms, in addition to the microfibril segments that are in direct contact

Enhancement of TbIII-CuII single-molecule magnet performance through structural modification

We report a series of 3d–4f complexes {Ln2Cu3(H3L)2Xn} (X=OAc−, Ln=Gd, Tb or X=NO3−, Ln=Gd, Tb, Dy, Ho, Er) using the 2,2′-(propane-1,3-diyldiimino)bis[2-(hydroxylmethyl)propane-1,3-diol] (H6L) pro-ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb2Cu3(H3L)2Xn} complexes is seen by changing the auxiliary ligands (X=OAc− for NO3−). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu-based single-molecule magnet. Ab initio CASSCF calculations performed on mononuclear TbIII models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the TbIII coordination environment (C4v versus Cs)

Immunoglobulin κ Chain Allotypes (KM) in Onchocerciasis

GM and KM allotypes, powerful tools for genetic characterization of human populations, have been shown to play an important role in genetic predisposition to some infectious diseases. Two diverse racial groups-Afro-Ecuadorians and Amerindians-living in a single restricted geographical area of Ecuador, appear to have different risk factors for acquisition and clinical expression of onchocerciasis, a disease caused by the filarial parasite Onchocerca volvulus. In this study, GM and KM allotypes were determined in 25 Afro-Ecuadorians and 24 Amerindians infected with Onchocerca volvulus (INF) and in putative immune individuals (PI). In Afro-Ecuadorians, the frequency of the homozygous KM 3 phenotype was significantly decreased in INF as compared with the PI group (20 vs. 68%; P = 0.0012), while the frequency of the heterozygous KM 1,3 phenotype was increased in INF as compared with the PI subjects (48 vs 9%; P = 0.0044). These results suggest that in Afro- Ecuadorians KM 3 is associated with a lower relative risk (resistance), whereas KM 1,3 is associated with an increased risk (susceptibility) of onchocerciasis

Worlds Beyond: A Strategy for the Detection and Characterization of Exoplanets Executive Summary of a Report of the ExoPlanet Task Force Astronomy and Astrophysics Advisory Committee Washington, DC June 23, 2008

[No abstract

From evaporative to cooling crystallisation:an initial co-crystallisation study of cytosine and its fluorinated derivative with 4-chloro-3,5-dinitrobenzoic acid

Two new multi-component molecular complexes of cytosine and 5-fluorocytosine with 4-chloro-3,5-dinitrobenzoic acid are presented. Materials synthesis was achieved initially by evaporative crystallisation and the crystal structures determined. The process was then successfully transferred into a controlled small scale cooling crystallisation environment, with bulk samples shown to be representative of the multi-component product phase, by powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC) methods. Turbidity measurements are shown to be a valuable process analytical technology probe for characterising the initial stages of molecular complex formation in solution. The significance of these findings for scale-up of crystallisation of multi-component molecular materials and for future transfer into continuous cooling crystallisation is discussed

Immunoarchitecture of the Regenerating Rat Spleen: Effects of Partial Splenectomy and Heterotopic Autotransplantation

To investigate the microstructure of in situ (eutopic) and autotransplanted (ectopic) splenic remnants, adult Sprague-Dawley rats were studied 60 days after 1) subtotal (~80%) splenectomy, 2) total splenectomy followed by single or multiple remnant intraperitoneal autotransplantation, or 3) sham operation. Total nucleated cell counts were determined in excised splenic remnants, and immunohistochemical staining using monoclonal antibodies to rat B-and T-cell antigens was performed in serial tissue sections. Immunoarchitecture of eutopic remnants was indistinguishable from that of intact spleens and total nucleated cell counts remained proportional to weight. In contrast, ectopic remnants showed sparsity and abnormal mixing of B and T lymphocyte subpopulations with widespread loss of follicles and periarteriolar lymphoid sheaths in addition to lower density and marked reduction of total nucleated cells. These findings provide immunohistologic evidence that preservation of intact vasculature is critical to splenic architecture, which may account in part for the demonstrable functional inferiority of ectopic remnants

Intermolecular hydrogen transfer and solubility tuning in multi-component molecular crystals of the API piroxicam

Twelve multi-component molecular crystals of the active pharmaceutical ingredient (API) piroxicam (PX) are described contrasting those with basic N-heterocycles with those formed with strong haloanilic acids. The effect on the solubility of this API is discussed, with evidence of enhanced solubility in the multi-component crystals formed.</p

Self-assembly synthesis of precursors to potential open framework alkali earth metal-organic complexes

A series of magnesium pyridinecarboxylic–dicarboxylic acid complexes, synthesised as precursors to potential framework materials, show a range of metal ligand and hydrogen bonding geometries. The pyridinedicarboxylic complexes show most promise as precursors for further syntheses.</p