Anti-HIV-1 gp120 aptamer-mediated small interfering (si)RNA delivery. (a) Schematic of the anti-HIV-1 gp120 aptamer-siRNA chimeras. The anti-gp120 aptamer binds to gp120 and the 27-mer Dicer substrate RNA duplex targets a common exon of the HIV-1 tat/rev transcript. Dicer processing results in 21-mer siRNAs that are incorporated into an RNA-induced silencing complex (RISC). (b) Schematic of the anti-HIV gp120 aptamer-'sticky bridge'-siRNA conjugates. Either the antisense or the sense strand of the 27-mer Dicer substrate RNA duplex and the aptamer were attached with to complementary 'sticky' sequences. After a simple annealing, they form stable base pairs.