A new method for the routine spreading of DNA in protein-free conditions

Graphene: Substrate preparation and introduction

This technical note describes the transfer of continuous, single-layer, pristine graphene to standard Quantifoil TEM grids. We compare the transmission properties of pristine graphene substrates to those of graphene oxide and thin amorphous carbon substrates. Positively stained DNA imaged across amorphous carbon is typically indiscernible and requires metal shadowing for sufficient contrast. However, in a practical illustration of the new substrates properties, positively stained DNA is imaged across pristine graphene in striking contrast without the need of metal shadowing. We go onto discuss technical considerations and the potential applications of pristine graphene substrates as well as their ongoing development.

The prion protein has DNA strand transfer properties similar to retroviral nucleocapsid protein

The transmissible spongiform encephalopathies are fatal neurodegenerative diseases that are associated with the accumulation of a protease-resistant form of the cellular prion protein (PrP). Although PrP is highly conserved and widely expressed in vertebrates, its function remains a matter of speculation. Indeed PrP null mice develop normally and are healthy. Recent results show that PrP binds to nucleic acids in vitro and is found associated with retroviral particles. Furthermore, in mice the scrapie infectious process appears to be accelerated by MuLV replication. These observations prompted us to further investigate the interaction between PrP and nucleic acids, and compare it with that of the retroviral nucleocapsid protein (NC). As the major nucleic acid-binding protein of the retroviral particle, NC protein is tightly associated with the genomic RNA in the virion nucleocapsid, where it chaperones proviral DNA synthesis by reverse transcriptase. Our results show that the human prion protein (huPrP) functionally resembles NCp7 of HIV-1. Both proteins form large nucleoprotein complexes upon binding to DNA. They accelerate the hybridization of complementary DNA strands and chaperone viral DNA synthesis during the minus and plus DNA strand transfers necessary to generate the long terminal repeats. The DNA-binding and strand transfer properties of huPrP appear to map to the N-terminal fragment comprising residues 23 to 144, whereas the C-terminal domain is inactive. These findings suggest that PrP could be involved in nucleic acid metabolism in vivo.

Occupational allergic contact dermatitis caused by 2,4,6-tris-(dimethylaminomethyl)phenol, and review of sensitizing epoxy resin hardeners

BACKGROUND

Epoxy resin compounds (ERC) include a large number of sensitizing chemicals such as epoxy resins (ER), hardeners (curing agents), and reactive diluents. Allergic contact dermatitis (ACD) caused by ERCS is often occupational.

MATERIALS AND METHODS

We report a patient, sensitized to a hardener of a two-component epoxy paint. Three conventional patch test sessions were performed to diagnose the causative chemical. We also review the literature on sensitizing epoxy-resin hardeners.

RESULTS

A 47-year-old nonatopic woman developed dermatitis from a two-component epoxy paint. Patch testing with epoxy resin was negative, but 2,4,6-tris(dimethylaminomethyl)phenol (tris-DMP), used in the paint hardener, induced an allergic patch test reaction. We also review briefly other epoxy hardeners that have caused allergic dermatitis, including: (1) aliphatic polyamines, e.g., ethylenediamine, diethylenetriamine, triethylenetetramine, 3-dimethylaminopropylamine, and trimethylhexamethylenediamine; (2) cycloaliphatic polyamines, e.g., isophoronediamine and 3,3'-dimethyl-4,4-diaminodicyclohexylmethane; (3) aromatic amines, such as 4,4'-diaminodiphenylmethane, m-phenylene diamine, and 1,3-xylylene diamine; (4) dicyanodiamide; (5) triglycidyl isocyanurate, an epoxy compound that may be used as an epoxy-resin hardener; and (6) additives in epoxy accelerators, such as hexavalent chromate.

CONCLUSIONS

No one chemical can be used to screen for sensitization to the many different epoxy hardeners. Extensive patch testing may be required to reveal the hardener that has caused the allergy. The hardener, 2,4,6-tris-(dimethylaminomethyl)phenol (tris-DMP), is a new sensitizer. To verify ACD caused by tris-DMP, patch-testing at 1% in petrolatum is suggested.

Striving for atomic resolution in biomolecular topography: the scanning force microscope (SFM)

The invention in 1986 of scanning force microscopy (SFM) provided a new and powerful tool for the investigation of biological structures. SFM yields a three-dimensional view at nanometer resolution of the surface topography associated with biological objects. The potential for imaging either macromolecules or biomolecules and cells under native (physiological) conditions is currently being exploited to obtain functional information at the molecular level. In addition, the forces involved in individual bimolecular interactions are being assessed under static and dynamic conditions. In this report we focus on the imaging capability of the SFM. The rather broad spectrum of applications represented is intended to orient the prospective user of biological SFM.

Structure of recombinant rat UBF by electron image analysis and homology modelling

We have studied the structure of recombinant rat UBF (rrUBF), an RNA polymerase I transcription factor, by electron microscopy and image analysis of single particles contrasted with methylamine tungstate. Recombinant rat UBF appeared to be a flat, U-shaped protein with a central region of low density. In the dominant projections, 2-fold mirror symmetry was seen, consistent with the dimerization properties of this molecule, and of dimensions in agreement with the length of DNA that rat UBF protects in footprinting studies. Electron microscopy of various rrUBF-DNA complexes confirmed that our recombinant protein was fully able to bind the 45S rDNA promoter, and that it caused substantial bends in the DNA. Upon extended incubation in a droplet covered by a lipid monolayer at the liquid-air interface, rrUBF formed long filamentous arrays with a railway track appearance. This structure was interpreted to consist of overlapping rrUBF dimers 3.5 nm apart, which value would represent the thickness of the protein. Our results show rrUBF to interact with and bend the promoter DNA into a roughly 10 nm diameter superhelix. Based on all these electron microscopical results, an atomic structure was predicted by homology modelling of the HMG fingers, and connected by energy minimized intervening segments.

The scanning force microscopy of DNA in air and in n-propanol using new spreading agents

We present recent advances in DNA specimen preparation technique for scanning force microscopy (SFM) based on spreading on mica in the presence of cationic and non-ionic detergents. Reproducible DNA imaging in air and in n-propanol has been achieved in the presence of the non-ionic detergent 2,4,6-tris(dimethylaminomethyl) phenol (DMP-30) or the cationic detergent cetylpyridinium chloride (CP) in a microdrop containing nanograms of DNA. In an alternative procedure, a microdrop of detergent is applied to the surface just prior to the DNA. Quantitative image analysis yields as the apparent molecular dimensions of the DNA a width of approximately 7 nm and a height of approximately 0.7 nm, and delineates the problems of DNA metrology by SFM.