Chemical and Enzymatic Methods for Preparing Circular Single‐Stranded DNAs

Small circular oligonucleotides can be used for diagnostic, therapeutic, and laboratory purposes. These systems have gained considerable attention in recent years because they form unusually strong and specific complexes with RNA and DNA strands. Synthetic circular DNAs of 20 to 200 nucleotides can also serve as catalysts for amplified DNA and RNA synthesis by a rolling circle mechanism. This unit presents methods for synthesizing small circular oligonucleotides. These simple "one-pot" procedures are carried out using short DNA splints that hold the circle together until it is chemically or enzymatically ligated.