POTENT AND SELECTIVE-INHIBITION OF GENE-EXPRESSION BY AN ANTISENSE HEPTANUCLEOTIDE

Factors that govern the specificity of an antisense oligonucleotide (O N) for its target RNA include accessibility of the targeted RNA to ON binding, stability of ON/RNA complexes in cells, and susceptibility of the ON/RNA complex to RNase H cleavage. ON specificity is generally p roposed to be dependent on its length. To date, virtually all previous antisense experiments have used 12-25 nt-long ONs. We explored the an tisense activity and specificity of short (7 and 8 nt) ONs modified wi th C-5 propyne pyrimidines and phosphorothioate internucleotide linkag es. Gene-selective, mismatch sensitive, and RNase H-dependent inhibiti on was observed for a heptanucleotide ON. We demonstrated that the fla nking sequences of the target RNA are a major determinant of specifici ty. The use of shorter ONs as anti-sense agents has the distinct advan tage of simplified synthesis. These results may lead to a general, cos t-effective solution to the development of antisense ONs as therapeuti c agents.