Figure 9.

Differences in the N channel between four human AGOs. (A) Pathways of guide and target strands. The domain color codes are the same as in Figure 3. The nucleic acid-binding cleft is colored in gray. (B) Transfer of the guide 3′ supplementary and tail regions between two branched channels. In the case of a 21 nt guide, the g2–g8 and g13–g16 serve as the target binding sites. (C) Y-shaped nucleic acid-binding cleft. The cleft is composed of the Seed-Central channel (SC channel in the red box), the PAZ channel (P channel in the magenta box), and the N channel (blue box). (D) Local structures unique to each AGO. cS7, 3SI and 4SI are localized in the N channel. The catalytic DEDH tetrad is depicted as scissors. AGO3-specific residues on its N domain are shown as orange stars. The residues undergoing post-translational modification are shown with their residue number (see Figure 10). (E) Model of expanding the 3′ supplementary region. When the guide lengths are 22 nt (top) and 23 nt (bottom), the g17 and the g17–g18 participate in target recognition as part of the 3′ supplementary region, respectively.