SnapShot: Posttranscriptional Gene Silencing

Double-strand (ds)RNAs that are taken up exogenously, formed during viral replication, or generated from aberrant cellular RNAs are cut into 21–23 nucleotide (nt) siRNAs by Dicer in association with dsRNA-binding (dsRBD) protein. The siRNAs are then loaded into RISC, a complex containing Argonaute (Ago) protein. After elimi-nation of the siRNA passenger strand, RISC pairs with cognate RNA via the siRNA guide strand and cuts its target using the slicer activity of Ago. In mammals and