[Enzymatic incorporation into oligonucleotides of modified nucleosides]

Behaviour of modified nucleosides, tRNA components, and their analogues has been studied in the internucleotide bond formation catalysed by ribonucleases of various substrate specificity, polynucleotide phosphorylases, and T4 RNA ligase and the results are summarised in this paper. Pseudouridine, dihydrouridine, ribothymidine, 5-methylcytidine, inosine, and 6-methyladenosine can participate in the reaction of internucleotide bond formation the presence of most ribonucleases used, viz. Pb2, Pcl2, Pb1, Pch1, C2, T1, pancreatic RNase. 3-Methylcytidine and 4-acetylcytidine form internucleotide bond (as phosphate acceptors) usually by means of guanyl-specific ribonucleases, whereas 1-methylandenosine is incorporated with ribonuclease Pel2. 7-Methylguanosine and 1-methylguynosine 2',3'-cyclophosphates can be used as phosphate donors in the presence of ribonuclease Pb2; in the similar enzymatic reaction 6-isopentenyladenosine is an uneffective acceptor.