Anthracene readily forms photoadducts, anthracene dimers, and this photodimerization reaction has been well characterized. In general, however, the reaction requires close proximity and certain spatial alignment of both reaction partners. DNA could provide an ideal scaffold for accelerating the photocyclic addition. We synthesized a number of anthracene-DNA conjugates. The sequences of the conjugates, 5'AntODNn and 3'AntODNn (the length of methylene linkers: n = 3 or 6), were designed to bind adjacent sequences of the template with the anthracene units directed such that they stacked with each other. The conjugates were only dimerized in the presence of the template by light irradiation. The efficiency was affected by one-base displacement in the template sequence.

We present the photochemical ligation of anthracene-ODN (oligodeoxyribonucleotide) conjugates through cycloaddition of anthracenes. Anthracene-DNA conjugates were synthesized by linking the 5'- or 3'-end of ODNs to the anthracene group. The sequences of the conjugates were designed to hybridize to neighboring sites on the target ODN with their anthracene units facing each other. When the ternary duplex consisting of the two conjugates and the target forms, the conjugates can be dimerized by light irradiation. The dimerization efficiency was affected by the substitution position of the anthracene group and by a one-base displacement in the template sequence. Furthermore, it is demonstrated that the capping of the duplex and connecting third strands in a triplex structure could also be the target of the photochemical ligation.

Much effort has focused on methods for detecting various genetic differences in individuals, including single nucleotide polymorphisms (SNPs). SNP can be characterized as a substitution, insertion, or deletion at a single base position on a DNA strand. There is expected to be on average one SNP for every 1000 bases of the human genome, and some variations located in genes are suspected to alter both the protein structure and the expression level. Therefore, highly sensitive techniques with a simple procedure would be desirable for a high-throughput screening of millions of SNPs widely dispersed throughout the human genome. In this short review, we consider recently reported unique techniques for genotyping in a homogeneous solution, and organize them in terms of the chemical and physical processes accelerated on DNA.

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The techniques of chemical ligation have attracted great attention as an alternative to enzymatic joining of DNA ends. Here we introduce the photoligation of anthracene-modified ODN conjugates through anthracene cyclodimer formation. The effect of the positions and the kinds of single base mismatch on the template was evaluated using eight templates with one-base displacements. We found out that the yield of the ligation was affected by mispairing in a positiondependent manner. Such results would be attributed to the disruption of the local structure at the ligation site.