Methods and compositions for enhancing the efficacy and specificity of single and double blunt-ended siRNA

Abstract

The present invention provides methods of enhancing the efficacy and specificity of RNAi using single or double blunt-ended siRNA. The invention also provides single and double-blunt ended siRNA compositions, vectors, and transgenes containing the same for mediating silencing of a target gene. Therapeutic methods are also featured.

What is claimed: 
     
       1. A method of silencing a target mRNA comprising providing a double stranded RNA (dsRNA) comprising a sense strand and an antisense strand, wherein the base pair strength between the antisense strand 5′ end (AS 5′) and the sense strand 3′ end (S 3′) is less than the base pair strength between the antisense strand 3′ end (AS 3′) and the sense strand 5′ end (S 5′), wherein said dsRNA comprises a frayed AS 5′, such that the antisense strand preferentially guides cleavage of a target mRNA, and wherein said S 3′ is lacking an overhang and wherein said AS 3′ comprises an overhang. 
     
     
       2. The method of  claim 1 , wherein the base pair strength is less due to at least one mismatched base pair between the AS 5′ and the S 3′ than between the AS 3′ and the S 5′. 
     
     
       3. The method of  claim 1 , wherein the mismatched base pair is selected from the group consisting of G:A, C:A, C:U, G:G, A:A, C:C, U:U, I:A, I:U, and I:C. 
     
     
       4. The method of  claim 1 , wherein the base pair strength is less due to at least one wobble base pair between the AS 5′ and the S 3′ than between the AS 3′ and the S 5′. 
     
     
       5. The method of  claim 4 , wherein the wobble base pair is G:U. 
     
     
       6. The method of  claim 1 , wherein each strand of the dsRNA has a length of between about 19 nucleotides and about 22 nucleotides. 
     
     
       7. The method of  claim 1 , wherein said dsRNA is provided as an shRNA which is processed by a cell to yield the dsRNA. 
     
     
       8. The method of  claim 7 , wherein a viral construct encodes the shRNA. 
     
     
       9. The method of  claim 1 , wherein the AS 3′ comprises a two nucleotide overhang. 
     
     
       10. The method of  claim 1 , wherein the AS 3′ comprises a dTdT overhang.