Cross-Linking versus Non-Cross-Linking Aggregation of Gold Nanoparticles Induced by DNA Hybridization: A Comparison of the Rapidity of Solution Color Change.

Gold nanoparticles densely modified with single-stranded DNA (ssDNA-AuNPs) form aggregates with cross-linker ssDNAs via duplex formation. Alternatively, the ssDNA-AuNPs are spontaneously aggregated at high ionic strength in a non-cross-linking manner when complementary ssDNAs are added to form fully matched duplexes. Both aggregation modes are accompanied by a red-to-purple color change, which has been exploited in various bioassays. The current study compares the rapidity of color change between the cross-linking and non-cross-linking aggregation modes under identical conditions. When a small number of cross-linker/complementary DNAs are provided, the cross-linking mode exhibited more rapid color change than the non-cross-linking mode. Conversely, with a large number of the DNAs, the non-cross-linking aggregation occurred more rapidly than the cross-linking counterpart. This finding allows one to select a more appropriate aggregation mode for application of ssDNA-AuNPs to colorimetric assays under given conditions.

Rapid Naked-Eye Discrimination of Cytochrome P450 Genetic Polymorphism through Non-Crosslinking Aggregation of DNA-Functionalized Gold Nanoparticles.

The front cover artwork is provided by the group of Tohru Takarada at RIKEN (Japan). The image shows a colorimetric single-nucleotide polymorphism (SNP) genotyping method that uses spontaneous aggregation of DNA-modified gold nanoparticles (DNA-AuNPs) for the simple and rapid SNP genotyping of the human cytochrome P450 2C19 monooxygenase gene. For more details, read the full text of the Full Paper at p. 508.

Rapid Naked-Eye Discrimination of Cytochrome P450 Genetic Polymorphism through Non-Crosslinking Aggregation of DNA-Functionalized Gold Nanoparticles.

Involvement of single-nucleotide polymorphism (SNP) genotyping in healthcare should allow for more effective use of pharmacogenomics. However, user-friendly assays without the requirement of a special instrument still remain unavailable. This study describes naked-eye SNP discrimination in exon 5 of the human cytochrome P450 2C19 monooxygenase gene, CYP2C19*1 (the wild-type allele) and CYP2C19*2 (the variant allele with G681A point mutation). The present assay is composed of allele-specific single-base primer extension and salt-induced aggregation of DNA-modified gold nanoparticles (DNA-AuNPs). Genetic samples extracted from human hair roots are subjected to this assay. The results are verified by direct sequencing. This study should promise the prospective use of DNA-AuNPs in gene diagnosis.

Analysis of the Rice ADP-Glucose Transporter (OsBT1) Indicates the Presence of Regulatory Processes in the Amyloplast Stroma That Control ADP-Glucose Flux into Starch.

Previous studies showed that efforts to further elevate starch synthesis in rice (Oryza sativa) seeds overproducing ADP-glucose (ADPglc) were prevented by processes downstream of ADPglc synthesis. Here, we identified the major ADPglc transporter by studying the shrunken3 locus of the EM1093 rice line, which harbors a mutation in the BRITTLE1 (BT1) adenylate transporter (OsBt1) gene. Despite containing elevated ADPglc levels (approximately 10-fold) compared with the wild-type, EM1093 grains are small and shriveled due to the reduction in the amounts and size of starch granules. Increases in ADPglc levels in EM1093 were due to their poor uptake of ADP-[(14)C]glc by amyloplasts. To assess the potential role of BT1 as a rate-determining step in starch biosynthesis, the maize ZmBt1 gene was overexpressed in the wild-type and the GlgC (CS8) transgenic line expressing a bacterial glgC-TM gene. ADPglc transport assays indicated that transgenic lines expressing ZmBT1 alone or combined with GlgC exhibited higher rates of transport (approximately 2-fold), with the GlgC (CS8) and GlgC/ZmBT1 (CS8/AT5) lines showing elevated ADPglc levels in amyloplasts. These increases, however, did not lead to further enhancement in seed weights even when these plant lines were grown under elevated CO2. Overall, our results indicate that rice lines with enhanced ADPglc synthesis and import into amyloplasts reveal additional barriers within the stroma that restrict maximum carbon flow into starch.