Synthetic double-stranded oligonucleotides for specific inhibition of gene expression

1. A double-stranded RNA oligonucleotide of Formula I

5′-(U)vX-(N)x-(W)-3′

3′-(Z)n-(N′)y-5′  Formula I

wherein

N and N′ are naturally occurring nucleotides bound by 3′,5′ internucleotide bonds, wherein a portion of the oligonucleotide is double-stranded between (N)x and (N′)y, and wherein the nucleotide strand (N)x, is sufficiently complementary to a target RNA to hybridize thereto and inhibit its expression through RNA interference, and wherein the nucleotide strand (N′)y is at least partially homologous to the target RNA, and wherein

N is selected from the group consisting of adenine (A), cytosine (C), guanine (G), and uracil (U);

x is independently 15-25;

y is independently 15-25;

n is independently 4 to 6;

v is independently 1 to 20, whereas: when v=1, X is selected from the group consisting of A, C, and G, and when v=2 to 20, X is absent;

W is selected from the group consisting of U2-20, UA, UC, and UG, or is absent; and Z is A; nucleotides of W being linked via a 3′,5′ internucleotide bond, and

wherein at least two nucleotides of Z are linked via a 2′,5′ internucleotide bond and are present in a single-stranded form that does not base pair with the target gene or with the RNA homologous thereto, thereby forming a 2′,5′ linked oligonucleotide residue on the 3′ end of the nucleotide strand (N′)y and wherein the internucleotide bonds in the double-stranded oligonucleotide are 3′,5′ or 2′,5′ internucleotide bonds.

2. The double-stranded RNA of claim 1 , wherein v is 2 to 10.

3. The double-stranded RNA of claim 2 , wherein v is 2 to 6.

4. The double-stranded RNA of claim 1 , wherein U 2-20 is U 2-10 .

5. The double-stranded RNA of claim 4 , wherein U 2-20 is U 2-6 .

6. The double-stranded RNA of claim 1 , wherein x is 16 to 23.

7. The double-stranded RNA of claim 6 , wherein x is 19 to 21.

8. The double-stranded RNA of claim 1 , wherein Z is adenosine or 3′-deoxyadenosine.

9. The double-stranded RNA of claim 1 , in which one or more natural phosphodiester bonds have been replaced by unnatural internucleotide bonds that stabilize against nuclease degradation.

10. The double-stranded RNA of claim 9 , in which one or more natural phosphodiester bonds have been replaced by phosphorothioate bonds.

11. The double-stranded RNA of claim 10 , in which a plurality of natural phosphodiester bonds have been replaced by phosphorothioate bonds, with said replacements being located on the 5′ or 3′ ends of the oligonucleotide, and on internal pyrimidine nucleotides of the oligonucleotide.

12. The double-stranded RNA of claim 1 , wherein one of nucleotide strands (N) x or (N′) y , is between 23 and 65 nucleotides in length and the other of the nucleotide strands is between 23 and 31 nucleotides in length.

13. The double stranded RNA of claim 1 , wherein the double stranded RNA comprises one or more 2′ O-methylribonucleotides.

14. The double stranded RNA of claim 1 , wherein the double stranded RNA comprises one or more 2′ fluoro-2′-deoxyribonucleotides.

15. The double stranded RNA of claim 1 , wherein the double stranded RNA comprises one or more locked nucleic acids (LNA).

16. The double stranded RNA of claim 1 , wherein the double stranded RNA further comprises a linker that links the two RNA strands.

17. The double stranded RNA of claim 16 , wherein the linker is a nucleotide linker.

18. The double stranded RNA of claim 16 , wherein the nucleotide linker comprises thymidine.

19. The double stranded RNA of claim 16 , wherein the nucleotide linker comprises 4-20 nucleotide residues.

20. The double stranded RNA of claim 19 , wherein the 4-20 nucleotide residues comprise one or more thymidines.

21. The double stranded RNA of claim 19 , wherein the 4-20 nucleotide residues are thymidines.

22. The double stranded RNA of claim 16 , wherein the nucleotide linker comprises 4-5 nucleotide residues.

23. The double stranded RNA of claim 22 , wherein the 4-5 nucleotide residues comprise one or more thymidines.

24. The double stranded RNA of claim 23 , wherein the 4-5 nucleotide residues are thymidines.

25. The double stranded RNA of claim 16 , wherein the linker is a non-nucleotide linker.