Patent ID: 8513207

Claim:
An isolated double stranded nucleic acid (dsNA) comprising a first oligonucleotide strand having a 5′ terminus and a 3′ terminus and a second oligonucleotide strand having a 5′ terminus and a 3′ terminus, wherein: said first strand is 31 to 49 nucleotide residues in length, wherein starting from the first nucleotide (position 1) at the 5′ terminus of the first strand, positions 1 to 23 of said first strand are ribonucleotides; said second strand is 31 to 53 nucleotide residues in length and comprises 23 consecutive ribonucleotides that base pair with the ribonucleotides of positions 1 to 23 of said first strand to form a duplex; the 5′ terminus of said first strand and the 3′ terminus of said second strand form a structure selected from the group consisting of a blunt end and a 1-4 nucleotide 3′ overhang; the 3′ terminus of said first strand and the 5′ terminus of said second strand form a duplexed blunt end; at least one of positions 24 to the 3′ terminal nucleotide residue of said first strand is a deoxyribonucleotide that base pairs with a deoxyribonucleotide of said second strand; and said second strand is sufficiently complementary to a target RNA along at least 19 ribonucleotides of said second strand length to reduce target gene expression when said double stranded nucleic acid is introduced into a mammalian cell.