Joining of ribooligonucleotides with T4 RNA ligase and identification of the oligonucleotide-adenylate intermediate

T4 RNA ligase was found to join A-A-A-A-A-A and 32pU-U-U-U in the presence of ATP as cofactor. In this reaction the pyrophosphate of pU-U-U-U and pA was isolated by chromatography on a RPC-5 column, besides the joined product and the starting materials. This pyrophosphate was shown to be an intermediate in the joining reaction because of the fact that coupling with A-A-A-A-A-A to give the decanucleotide could be performed in the absence of ATP. The structure of the oligonucleotide-adenylate was determined by enzymatic digestion with base-nonspecific nuclease and venom phosphodiesterase. Futher evidence for the proposed structure was obtained by isolation of the intermediate obtained by using pU-U-U-U and [alpha-32p]ATP. This pyrophosphate gave pA and pU by treatment with venom phosphodiesterase. Several other joining reactions between various purine- and pyrimidine ribooligonucleotides to 5'-phosphorylated ribooligonucleotides are discussed.