Catalysis of DNA joining by bacteriophage T4 RNA ligase

Abstract RNA ligase, purified extensively from Escherichia coli infected with wild-type or DNA ligase mutants of bacteriophage T4, catalyzes the joining of 5′-phosphoryl terminated DNA to DNA and RNA acceptors. This was shown by the conversion of [5′- 32 P]deoxyoligomers to a form resistant to phosphatase, the increased chain length of the joined RNA-DNA copolymers, the circularity of the DNA joined product, and the transfer of the 5′- 32 P label of the donor DNA to the 3′-end of both RNA and DNA acceptors. The novel DNA joining activity is intrinsic to RNA ligase since it co-purifies with RNA joining activity and has the same requirements, inhibitors, and thermolability. These results suggest that RNA ligase should be a useful reagent for the synthesis of defined sequence DNA and RNA-DNA copolymers and raise the possibility of a role for RNA ligase in DNA metabolism.