In vitro selection was used to isolate a series of deoxyribozymes from a pool of random-sequence DNAs that catalyze an ATP-dependent self-capping reaction. Each deoxyribozyme catalyzes the transfer of the nucleoside and a-phosphate moieties of ATP to the phosphate group located at its 5' terminus, thereby creating a 5\5'-pyrophosphate cap. This same pyrophosphate cap structure is formed by T4 DNA ligase during the classical process of DNA ligation. These DNA capping enzymes representative of a

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... ollection of self-processing deoxyribozymes that can be used for the directed modification of DNA.