INHIBITION OF T4 POLYNUCLEOTIDE KINASE-ACTIVITY BY PHOSPHOROTHIOATE AND CHIMERIC OLIGODEOXYNUCLEOTIDES

Whole and partially modified phosphorothioate oligodeoxynucleotides (O DN) were found to directly inhibit T4 polynucleotide kinase (PNK) acti vity, while phosphodiester ODN showed no detectable inhibition. This i nhibition was found to be length dependent, as demonstrated by a 28-me r phosphorothioate ODN with an IC50 of 12 nM, and an 8-mer phosphoroth ioate ODN with an IC50 of 27,000 nM. Inhibition depended on the number and type of modified internucleotide linkages: a 20-mer phosphorothio ate ODN had an IC50 of 21 nM, while a chimeric ODN with seven phosphor othioate linkages and an identical sequence showed no inhibition. On t he other hand, the same sequence as a chimeric phosphorodithioate ODN (with seven dithioate linkages) had an IC50 of 580 nM. Four different chimeric phosphorodithioate ODN showed markedly different potencies of inhibition, suggesting that inhibition of PNK activity can be sequenc e specific.