A double-stranded RNA comprising an antisense RNA and a sense RNA with
specific mutations are disclosed as having enhanced RNAi activities. The
double stranded RNA has at least one substitution or insertion mutation
introduced at a first, second or third nucleotide position from the 5'
end of the antisense RNA or at 17-19 position as counted from the 3' end
of the antisense sequence excluding an overhang, and the antisense RNA is
complementary to a region of an mRNA of a target gene except the at least
one substitution or insertion mutation. Related single-strand RNAs,
vectors, methods, cells and compositions are disclosed.
