Figure 8.

Model of an sciRNA:Ago2 complex suggests that a circular sense strand can be accommodated. The model is based on the crystal structure of Ago2 bound to a duplex siRNA with seed region pairing (54). Carbon atoms of the sense strand (nucleotides S13–S21) are colored in yellow, and carbon atoms of the antisense strand (nucleotides AS1-AS9) are in green. The Z linker carbons are highlighted in cyan. Selected side chains of the Ago2 PIWI and MID domains and the L2 linker region (tan ribbon) are labeled. The view is across the major (top) and minor grooves (bottom) of the seed region duplex.