- Exploration of the limits of biocatalysis has led to the discovery that DNA has significant potential for enzymatic function. This makes possible the construction of DNA enzymes or "deoxyribozymes" for catalyzing various chemical reactions that could be used to address fundamental questions in biocatalysis or that could find unique applications in biotechnology. Of significant interest are self-modification reactions, given the fundamental role that DNA serves in modern living systems. Recently, in vitro selection strategies have been used to isolate prototypical ATP-dependent deoxyribozymes from random-sequence populations of DNA that catalyze DNA phosphorylation and others that catalyze DNA adenylation. In nature, protein enzymes such as T4 DNA kinase and T4 DNA ligase catalyze identical chemical reactions. These findings suggest that DNA constructs could be engineered to efficiently catalyze other self-modifying reactions, including ATP-dependent DNA ligation. This article provides a detailed overview of the methods used to isolate deoxyribozymes that promote ATP-dependent DNA ligation.