2 T4 RNA Ligase

T4 RNA ligase catalyzes the circularization of homopolyribonucleotides with a 3′-terminal hydroxyl and a 5′-terminal phosphate through the formation of a 3′ →5′ phosphodiester bond, with hydrolysis of adenosine triphosphate (ATP) to adenosine monophosphate (AMP) and pyrophosphate (PPi). It also carries out intermolecular reactions with either RNA or DNA. The removal of internal sequences from primary transcripts of some eukaryotic tRNAs and mRNAs also involve the intermolecular joining of RNA molecules. This chapter focuses on the T4 enzyme, which is the only bacteriophage RNA ligase that has been purified to homogeneity and studied extensively. It illustrates the reaction mechanism and biological functions of the enzyme and briefly describes its applications in nucleic acid chemistry. T4 RNA ligase is essentially used in two general areas: the synthesis of oligonucleotides and the modification of RNA molecules. The remarkably broad substrate specificity of RNA ligase permits subtle future applications in RNA synthesis and its modification.