Nanogold may not glitter, but its presence significantly improves the specificity and yield of PCR reactions owing to the greater affinity of gold nanoparticles to single-stranded DNA than to double-stranded DNA which helps to reduce mispairing. Indeed, gel electrophoresis shows a single predominant band for the target DNA obtained by this method, in contrast to streaking bands for products obtained by conventional PCR (lanes 1 and 2; see image).
The finished sequence of the human genome still contains 260 euchromatic gaps. All the PCR-based genome walking techniques used to close gaps have common limitations, such as low efficiency and low specificity. We herein describe a strategy to solve this problem by employing gold nanoparticles (AuNPs) to improve the efficiency in primer walking amplification. We used this strategy to close a gap in human chromosome 5 containing a DNA stretch composed of the 12SAT repeat. The obtained gap sequence is highly conserved among several mammalian genomes. The demonstrated AuNP-assisted primer walking strategy is capable of effectively improving the specificity of PCR amplification and enriching the yield of target DNA fragments; it offers a new avenue for closing gaps left by current sequencing methods.
B. Song, X. Gao, F. Huang et al. describe in their Communication on page 6358 ff. the ability of Al ions to induce the formation of backbone ring structures in a wide range of peptides, including neurodegenerative disease related motifs.
Poly(vinylidene fluoride) (PVDF) is a polymorphic semicrystalline polymer. To utilize its piezo-, pyro-, and ferroelectric applications, it is ideal to fabricate the polar phases directly. Another way to obtain a polar PVDF is to transform the original nonpolar α crystals into their polar γ counterparts through the solid α–γ′ phase-transition. Therefore, a better understanding of the solid α–γ′ phase-transition is of great importance and significance. Here, the PVDF α–γ′ phase-transition process has been tracked in situ in real space using a polarized optical microscope based on the synchronous phase-transition accompanied by the change in birefringence. Thus, the propagation of the phase-transition along and perpendicular to the radial directions of the spherulites was quantitatively determined. It is found that the phase transition along the radial direction is almost 3 times faster than that in the tangential direction (1.07 vs 0.39 μm/min). Moreover, the effect of the crystallization temperature and subsequent annealing temperature on the phase-transition behavior has been explored. It is confirmed that annealing at a high temperature below the onset melting temperature provides thermal energy for the phase-transition and thus endows a high phase-transition efficiency and speed. The transition speed decreases, however, when the annealing temperature is close to the peak melting temperature. This is associated with the melting of the lamellae, which is adverse to the transformation of TGTG′ to T3GT3G′ conformation and consequently hinders the phase-transition. It is further demonstrated that the crystallization temperature of the sample affects the solid α–γ′ phase-transition in the subsequent annealing process as well. The sample crystallized at a higher temperature with an increased crystallinity and thickened lamellae facilitate the phase-transition. These results provide more insight into the solid α–γ′ phase-transition of PVDF.
Recently, the isolation and biochemical analysis of DNA at the single-molecule level has been recognized as very important for genetic research and clinical analysis. A unique technique for the positioning, dissection, and isolation of single DNA molecules using atomic force microscopy (AFM) has been demonstrated. Full-length genome DNA molecules were first deposited and stretched by a modified "molecular combing" technique onto a 3-aminopropyl triethoxysilane-coated mica substrate. A single DNA fragment was dissected from one of those genome DNA strands with the AFM tip at the desired position, and then isolated (or picked up) after a special operation called "kneading". All the operations including imaging, dissection, and isolation could be carried out with one tip. The isolated DNA fragment on the AFM tip could be successfully amplified by single-molecule PCR.
Abstract A combination of ab initio calculations, circular dichroism, nuclear magnetic resonance, and X‐ray photoelectron spectroscopy has shown that aluminum ions can induce the formation of backbone ring structures in a wide range of peptides, including neurodegenerative disease related motifs. These ring structures greatly destabilize the protein and result in irreversible denaturation. This behavior benefits from the ability of aluminum ions to form chemical bonds simultaneously with the amide nitrogen and carbonyl oxygen atoms on the peptide backbone.
Favorable binding of gold nanoparticles to single‐stranded DNA decreases the likelihood of mispair formation during annealing and clearly increases the specificity and yield of PCR, one of the most important standard methods of molecular biology. In their Communication on pp. 5100 ff., Z. Zhang, C. Fan, J. Hu, and co‐workers report on this promising field of biotechnology. (Xiaobin Wang assisted in the production of this image.)
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