Substantial effort has been placed on developing semiconducting carbon nanotubes and nanowires as building blocks for electronic devices--such as field-effect transistors--that could replace conventional silicon transistors in hybrid electronics or lead to stand-alone nanosystems. Attaching electric contacts to individual devices is a first step towards integration, and this step has been addressed using lithographically defined metal electrodes. Yet, these metal contacts define a size scale that is much larger than the nanometre-scale building blocks, thus limiting many potential advantages. Here we report an integrated contact and interconnection solution that overcomes this size constraint through selective transformation of silicon nanowires into metallic nickel silicide (NiSi) nanowires. Electrical measurements show that the single crystal nickel silicide nanowires have ideal resistivities of about 10 microOmega cm and remarkably high failure-current densities, >10(8) A cm(-2). In addition, we demonstrate the fabrication of nickel silicide/silicon (NiSi/Si) nanowire heterostructures with atomically sharp metal-semiconductor interfaces. We produce field-effect transistors based on those heterostructures in which the source-drain contacts are defined by the metallic NiSi nanowire regions. Our approach is fully compatible with conventional planar silicon electronics and extendable to the 10-nm scale using a crossed-nanowire architecture.

Single-crystal metallic nanowires and metal/semiconductor nanowire heterostructures

tRNA biology has come of age, revealing an unprecedented level of understanding and many unexpected discoveries along the way. This review highlights new findings on the diverse pathways of tRNA maturation, and on the formation and function of a number of modifications. Topics of special focus include the regulation of tRNA biosynthesis, quality control tRNA turnover mechanisms, widespread tRNA cleavage pathways activated in response to stress and other growth conditions, emerging evidence of signaling pathways involving tRNA and cleavage fragments, and the sophisticated intracellular tRNA trafficking that occurs during and after biosynthesis.

/pdf/trna-biology-charges-to-the-front-4a28s6q74p.pdf

tRNA biology charges to the front

The alarmones guanosine tetraphosphate and guanosine pentaphosphate (collectively referred to as (p) ppGpp) are involved in regulating growth and several different stress responses in bacteria. In ...

Recent functional insights into the role of (p)ppGpp in bacterial physiology

The role of guanosine 5'-triphosphate in polypeptide chain elongation.

Electron paramagnetic resonance (EPR) spectroscopy provides a variety of tools to study structures and structural changes of large biomolecules or complexes thereof. In order to unravel secondary structure elements, domain arrangements or complex formation, continuous wave and pulsed EPR methods capable of measuring the magnetic dipole coupling between two unpaired electrons can be used to obtain long-range distance constraints on the nanometer scale. Such methods yield reliably and precisely distances of up to 80 A, can be applied to biomolecules in aqueous buffer solutions or membranes, and are not size limited. They can be applied either at cryogenic or physiological temperatures and down to amounts of a few nanomoles. Spin centers may be metal ions, metal clusters, cofactor radicals, amino acid radicals, or spin labels. In this review, we discuss the advantages and limitations of the different EPR spectroscopic methods, briefly describe their theoretical background, and summarize important biological applications. The main focus of this article will be on pulsed EPR methods like pulsed electron-electron double resonance (PELDOR) and their applications to spin-labeled biosystems.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S003358350700460X

Long-range distance determinations in biomacromolecules by EPR spectroscopy.

Publisher Summary This chapter discusses that the adaptor role of tRNA requires that it has at least two functionally different sites-one for the specific interaction with the messenger, and one for accepting and transferring the particular amino acid to the growing polypeptide chain. The codon recognition mechanism of tRNA is explained in principle by the codon–anticodon interaction, including the wobble hypothesis, and has been confirmed by sequencing many tRNAs. The second function discusses that apart from the long-known fact that the -N-C-C-A end, common to all tRNAs, carries the amino acid in ester linkage, the problem of the specific attachment of an amino acid to its corresponding tRNA (the “recognition” problem) is still not solved. The chapter reviews that the -N-C-C-A end is not responsible for the specificity of the attachment; there must be other features in the molecule or in the enzymic mechanism of aminoacylation responsible for this high degree of specificity. However, these characteristics, whatever they are, must be seen in relation to the -N-C-C-A end, since this part of the tRNA carries the amino acid. Thus the presence of an intact -N-C-C-A end is a general prerequisite for the aminoacylation and for amino-acid transfer. It discusses the structural and the chemical requirements for the functioning of the -N-C-C-A terminus. The chapter summarizes recent results on the function of the -N-C-C-A end of tRNA as a reactive site during aminoacylation and ribosomal protein biosynthesis, with information about the structure of -N-C-C-A end and changes in its function after its modification.

The -C-C-A end of tRNA and its role in protein biosynthesis.

The involvement of 5S RNA in the binding of tRNA to ribosomes

Structural analogues of adenosine 5′-triphosphate and cytidine 5′-triphosphate were investigated as substrates for ATP(CTP): tRNA nucleotidyl transferase. Eight out of 26 ATP analogues and six out of nine CTP analogues were incorporated into the 3′ terminus of tRNA. In general, for the recognition of the substrates the modification of the cytidine is less critical than is the modification of adenosine. An isosteric substitution on the ribose residue is possible in both CTP and ATP. The free hydroxyls of these triphosphates can be replaced by an amino group or hydrogen atom without loss of substrate properties. Modifications of positions 1, 2, 6 and 8 on the adenine ring of ATP are not allowed whereas modification on positions 2, 4 and 5 on the cytosine ring of CTP are tolerated by the enzyme. No differences can be observed in the substrate properties of ATP(CTP): tRNA nucleotidyl transferase isolated from different sources. Methods for preparation of tRNA species, which are shortened at their 3′ end by one or more nucleotides, and analytical procedures for characterisation of these modified tRNAs are described.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1977.tb11985.x

Enzymatic Incorporation of ATP and CTP Analogues into the 3′ End of tRNA

In order to elucidate the functional role of the modified uridines at position 54 of tRNA, the 270 MHz high-field proton NMR spectra of methionine tRNAs from E. coli, from a mutant thereof, and from T. thermophilus, containing ribothymidine, uridine and 2-thioribothymidine, respectively, have been measured as a function of temperature. A comparison of the NMR melting profiles of the minor nucleosides from these tRNAs shows that the melting temperature of uridine containing tRNA is 6 degrees C lower than that of the wild type tRNA whereas that of the 2-thioribothymidine tRNA is 7 degrees C higher than that of the wild type tRNA. These results, therefore, demonstrate that these modifications serve for stabilization of the tertiary structure of tRNA.

Role of ribothymidine in the thermal stability of transfer RNA as monitored by proton magnetic resonance

The tetranucleotide TpψpCpGp binds to 50S ribosomal subunits and by doing so inhibits EF-Tu-directed aminoacyl-tRNA binding, EF-Tu-linked GTP hydrolysis and ribosome-dependent synthesis of magic spot I.

Mathias Sprinzl

Papers

The -C-C-A end of tRNA and its role in protein biosynthesis.

The involvement of 5S RNA in the binding of tRNA to ribosomes

Enzymatic Incorporation of ATP and CTP Analogues into the 3′ End of tRNA

Role of ribothymidine in the thermal stability of transfer RNA as monitored by proton magnetic resonance

Specific Recognition of GTψC Loop (Loop IV) of tRNA by 50S Ribosomal Subunits from E. coli