DGR mutagenic transposition occurs via hypermutagenic reverse transcription primed by nicked template RNA.

Diversity-generating retroelements (DGRs) are molecular evolution machines that facilitate microbial adaptation to environmental changes. Hypervariation occurs via a mutagenic retrotransposition process from a template repeat (TR) to a variable repeat (VR) that results in adenine-to-random nucleotide conversions. Here we show that reverse transcription of the Bordetella phage DGR is primed by an adenine residue in TR RNA and is dependent on the DGR-encoded reverse transcriptase (bRT) and accessory variability determinant (Avd ), but is VR-independent. We also find that the catalytic center of bRT plays an essential role in site-specific cleavage of TR RNA for cDNA priming. Adenine-specific mutagenesis occurs during reverse transcription and does not involve dUTP incorporation, indicating it results from bRT-catalyzed misincorporation of standard deoxyribonucleotides. In vivo assays show that this hybrid RNA-cDNA molecule is required for mutagenic transposition, revealing a unique mechanism of DNA hypervariation for microbial adaptation

A general lithography-free method of microscale/nanoscale fabrication and patterning on Si and Ge surfaces

Here, we introduce and give an overview of a general lithography-free method to fabricate silicide and germanide micro-/nanostructures on Si and Ge surfaces through metal-vapor-initiated endoepitaxial growth. Excellent controls on shape and orientation are achieved by adjusting the substrate orientation and growth parameters. Furthermore, micro-/nanoscale pits with controlled morphologies can also be successfully fabricated on Si and Ge surfaces by taking advantage of the sublimation of silicides/germanides. The aim of this brief report is to illustrate the concept of lithography-free synthesis and patterning on surfaces of elemental semiconductors, and the differences and the challenges associated with the Si and the Ge surfaces will be discussed. Our results suggest that this low-cost bottom-up approach is promising for applications in functional nanodevices

Morphology Instability Of Silicon Nitride Nanowires

We report that cylinder-shaped Si 3N 4 nanowires are not stable and can gradually transform into nanobelts via surface diffusion during high-temperature annealing. We demonstrate that such instability is driven by the requirements for reducing overall surface energy. The resultant nanobelts have the same width-to-thickness ratio, suggesting a stable morphology. A model in terms of surface energy is proposed to explain the formation of such stable morphology, which agrees well with experimental results. Our result suggests that instability could be a limiting factor for high-temperature applications of 1D nanostructures. © 2009 American Chemical Society

Single-Crystal Aln Nanonecklaces

Distinct single-crystal aluminum nitride nanonecklaces with uniform faceted beads are synthesized via catalyst-assisted nitriding of Al. The detailed morphology and structure of the nanonecklaces have been characterized. The growth process has been investigated by comparing the products obtained at different synthesis times. The results reveal that the formation of the nanonecklaces is via a process consisting of facet formation and bead unification. The formation of the facets is due to the presence of a liquid phase that lowers the surface tension of otherwise high-energy planes. The bead unification is driven by minimizing the energy contributed by surface energy and electrostatic energy. The unique morphology of the nanonecklaces could be useful for studying fundamental physical phenomena and fabricating nanodevices. © IOP Publishing Ltd

SUPPORT EFFECT ON THE STRUCTURE AND PROPERTIES OF MANGANESE OXIDE ELECTRODE MATERIALS

The composite electrode material of manganese oxide supported on poly glucose (PGS) was prepared by using KMnO4 as manganese source. In order to study the influence of the support on the structure and properties of the composite electrode materials, the changes of the composition of the composite electrode materials were investigated in different weight ratio of KMnO4/PGS (3:1, 3:3, 3:5, 3:7, 3:9). The characterization results of XRD, Raman special and XPS indicated the composition of manganese oxides was greatly influenced by the content of PGS. When the PGS content is lower, the composition of manganese oxide in hybrid material is single-component oxide (MnOOH or Mn3O4). With the increasing PGS content, a mixture of Mn3O4 and MnCO3 was observed, furthermore proportion of MnCO3 in mixture also increased, and up to higher PGS content (KMnO4/PGS=3:9), single-component MnCO3 was founded on hybrid material. In addition, the change of composition of hybrid materials also led to an obvious difference in electrochemical performance. With the increase of PGS content, the specific capacitance of hybrid materials increases firstly, and reaches the maximum with the weight ratio of KMnO4/PGS equal to 3:3, and then gradually decreases. This was attributed to the higher electrochemical performance of Mn3O4 than that of MnOOH and MnCO3

Bundled Silicon Nitride Nanorings

Bundled nanorings composed of several self-coiled nanowires are synthesized by catalyst-assisted pyrolysis of a polymeric precursor. Microstructural observation reveals that the nanowires have a bilayer structure consisting of a thin single-crystal Si3N4 layer and a thick amorphous layer. The thickness ratio of the two layers is ∼ 1:2, regardless of the nanowire size. The formation of the thick amorphous layer is likely due to the high A1 concentration within the precursor. The self-coiling mechanism is discussed and attributed to the difference in growth rates of the two layers. A phenomena model is proposed to account for the formation of the nanoring structure. © 2008 American Chemical Society

Asymmetric Silicon Nitride Nanodendrites

We have demonstrated the growth of asymmetric ordered Si3N 4 nanodendrites via the catalyst-assisted pyrolysis of a polymeric precursor. The growth of the unique structure is due to the usage of a co-catalyst composed of a Fe-Al mixture. First, Si3N4 stems grow at an early stage via a gas-solid process with Al being the catalyst. Fe is then selectively deposited on the negatively charged (010) surface of the Si3N4 stem to form catalytic droplets which promote the growth of the ordered nanowire branches. The novel nanostructures could be useful for the fabrication of nanodevices and nanocomposites. The principle demonstrated here is applicable for synthesizing ordered branched nanodendrites in other material systems. © 2008 American Chemical Society