An engineered RNA precursor capable of inducing RNA interference (RNAi) in vivo comprising(i) a first stem portion comprising a sequence of about 18 to 40 nucleotides that is complementary to a sequence of a messenger RNA (mRNA) of a target gene；(ii) a second stem portion comprising a sequence of about 18 to 40 nucleotides that is sufficiently complementary to the first stem portion to hybridize with the first stem portion to form a duplex stem； and(iii) a loop portion that connects the two stem portions；wherein the stem portion sequences of the duplex stem are from a wild-type stRNA (or miRNA) precursor but include the sequences of an siRNA duplex,such that the engineered RNA precursor, when processed in the cell, generates the siRNA duplex, thereby inducing RNAi of the mRNA of the target gene in the cell.
