Enzymatic synthesis of oligonucleotides of defined sequence. Addition of short blocks of nucleotide residues to oligonucleotide primers.

Polynucleotide phosphorylase from Escherichia coli can be used to catalyse the addition of short tracts of deoxyadenylate residues to the 3'-termini of deoxyribooligonucleotides of the type pdAn-dN (where dN = dC, dT or dG) using dADP as donor. Similarly, the enzyme can also be used to catalyse the addition of short tracts of adenylate residues to the 3'-termini of ribooligonucleotides of the type An-N (where N = C, U or G) using ADP as donor. In the ribooligonucleotide series, phosphorolytic cleavage of the primer oligonucleotides is significant and results in the concommitant production of oligoadenylates lacking the N residue. Oligomers of the same length, with and without the residue N, were readily separated by thermal elution from cellulose-pdT9 columns. This latter procedure therefore provides a simple method for purification of the oligoadenylates containing an internal base substitution and it also provides a convenient assay for oligonucleotide phosphorolysis.