Abstract:

SINGLE-STRANDED DNA can fold into well-defined sequence-dependent tertiary structures that specifically bind a variety of target molecules1–10, raising the possibility that some folded single-stranded DNAs might exhibit catalytic activities similar to those of ribozymes and protein enzymes. Derivatives of the hammerhead ribozyme that contain a majority of deoxyribonucleotides retain the ability to cleave RNA11, and a 'deoxyribozyme' was generated by leaving all essential ribonucleotides of the hammerhead on the RNA 'substrate'12. Recently in vitro selection has been used to isolate a DNA sequence that shows Pb2+-dependent RNA-cleaving activity13. Here we report the isolation by in vitro selection14–17 of a small single-stranded DNA that is a Zn2+/Cu2 +-dependent metalloenzyme. The enzyme catalyses the formation of a new phos-phodiester bond by the condensation of the 5′–hydroxyl of one oligodeoxynucleotide and a 3′-phosphorimidazolide on another oli-godeoxynucleotide, and shows multiple turnover ligation.