than one or perhaps two rna cleaving functionalities to oligonucleotide compositions in accordance with this invention in order to provide the benefits of the invention thus an rna cleaving moiety will preferably be tethered to a relatively small proportion of the subunits generally only one or two comprising the oligonucleotide compositions which is the targeting portion of the compositions of the invention in other embodiments of the invention however all of the nucleotides in an oligonucleotide can be modified to include one or more rna cleaving moiety groups the half life of the perfectly formed duplex will be greatly effected by the positioning of the tethered functional group inappropriate positioning of functional groups such as placement on the watson crick base pair sites would preclude duplex formation other attachment sites may allow sequence specific binding but may be of such low stability that the reactive functionality will not have sufficient time to initiate rna disruption it is believed that attaching rna cleaving moieties in accordance with the foregoing considerations will permit those moieties to lie in the minor groove of the hybrid formed from the composition of the present invention and the messenger rna for which modulation is desired it is possible that other positions for attachment of the rna cleaving moieties having a similar effect may be found especially when further modifications of the purine structure is undertaken as may be done by persons of ordinary skill in the art without deviating from the spirit of the present invention once again it is to be understood that preferably one or at most a few rna cleaving moieties are generally to be employed thus artisans in the field will have great latitude in selecting means of attachment of the rna cleaving moieties the pharmacodynamic improving group or the pharmacokinetic.