Schematic illustration of the design of effective siRNAs.

All residues of siRNA (filled or open circles) corresponded to those of the target mRNA sequences, except for the 3′ overhangs of the sense strand. In addition, the following conditions were preferred: (A) siRNAs with a GC content that ranged between 35% and 55%; (B) the 5′-sense end of siRNAs was G or C [7]; (C) the 5′-antisense end of siRNAs was A or U [7]; (D) the target position selected was located 75 bp downstream of the initiation codon (AUG), to avoid binding sites for translational factors [13]; (E) a GC content of 50% was preferred in the 12 bp sequences flanking the target position [14, Japan Bio Services Co.,LTD.(JAPAN) unpublished data]; (F) presence more than 3 nt of A or U residues in a 7 nt sequence at the 5′ end of the antisense strand of siRNA [7]; (G) the 2 nt overhangs of the antisense strand at the 3′ end were UU [15]; and (H) the 2 nt overhangs of the sense strand at the 3′ end were UU, UN, NU, or AA [15, Japan Bio Services Co.,LTD.(JAPAN) unpublished data].