Method of site-specific alteration of RNA and production of encoded polypeptides

A method of site-specific cleavage of a target RNA segment of an RNA molecule consisting essentially of combining the RNA molecule, in the presence of RNase H, with a mixed phosphate backbone oligonucleotide which is complementary to all or a portion of the RNA molecule wherein the mixed phosphate backbone oligonucleotide has an internal segment which activates RNase H and two flanking nucleotide sequences which are unable to activate RNasc H, one of the two flanking nucleotide sequences being present on either side of the internal segment, and wherein the internucleoside bridging phosphate residues of the internal segment are modified phosphates which are phosphorothioates and the internucleoside bridging phosphate residues of the two flanking modified nucleotide sequences are modified phosphates selected from the group consisting of methyl phosphonates, phosphoromorpholidates, phosphoropiperazidates, and phosphoramidates, under conditions appropriate for hybridization of complementary nucleotide sequences and activation of RNase H, thereby cleaving the target RNA segment.