ANTISENSE PHOSPHOROTHIOATE OLIGONUCLEOTIDES DIRECT BOTH SITE-SPECIFICAND NONSPECIFIC RNASE-H CLEAVAGE OF IN-VITRO SYNTHESIZED P120 MESSENGER-RNA

To determine the sequence specificity with which various antisense pho sphorothioate oligonucleotides to the p120 gene could direct RNAse H-d ependent cleavage of p120 mRNA, an in vitro RNAse H assay was done on in vitro synthesized p120 mRNA. Three oligonucleotides tested (ISIS 34 62, coding region; ISIS 3466, 3' untranslated region; and ISIS 3782, 3 ' untranslated region) directed cleavage of p120 mRNA at the target si tes. In addition, several additional cleavage products from nontarget sites were detected. A computer sequence homology search revealed that these additional bands probably result from cleavage at regions of co mplementarity of eight or nine contiguous bases of the oligonucleotide and the p120 mRNA. These findings suggest that such nontarget specifi c cleavages may account for multiple effects of phosphorothioate oligo nucleotides.