Construction of circular oligodeoxyribonucleotides on the structural basis of i-motif

Abstract

As illustrated in Figure A-1, it was discovered for the first time that beyond the scope of the duplex and triplex strategies, the i-motif, a four stranded assembly based on C+.C base pairs formed under a slightly acidic condition, can direct the sequence-specific formation of a phosphodiester linkage between 3' hydroxyl group and 5' phosphate group of linear oligodeoxyribonucleotides with high efficiency and high sequence-selectivity by chemical activation and thus represents a new type of structural template for constructing circular oligodeoxyribonucleotides. Based on this new strategy, a 28-mer circular oligodeoxyribonucleotide has been successfully constructed on intramolecular i-motif structure, exonuclease VII, exonuclease I and Alkaline Phosphatase digestion have confirmed the circular nature of this product. Furthermore, i-motif structure has been demonstrated as the real intermediate of the circularization process via studying the relation between yield of circular products and factors influencing the i-motif structure formation. Furthermore, when this conception was applied to the bimolecular i-motif structure, circular oligodeoxyribonucleotide possessing as few as 9 nucleotides, the smallest template-directed synthetic oligodeoxyribonucleotide achieved up to now, has been prepared. In conclusion, utilization of the unique self-recognition pattern of the i-motif in the current study not only represents a distinctive strategy for constructing circular oligonucleotides but also opens up a new method for the synthesis of oligonucleotide sequences which are not accessible via other methodologies.