Figure 4.

Maturation of the L1-Stalk Segment Is Linked to “Foot” Remodeling

(A) The L1 segment (rRNA helices H74–H79, gold) is stabilized in a pre-mature conformation by a set of AFs, including Ebp2 (green), Nip7 (magenta), Noc3 (purple), Nop2 (brown), and Nsa2 (turquoise).

(B) The L1 segment undergoes large-scale conformational changes during maturation, which requires an outward rotation of the Rlp7 N-terminal α helix. The conformations as observed in states D and E of the L1 segment and Rlp7 are colored in gold and turquoise. Gray denotes their conformation as observed in state F.

(A and B) Helices H76–H79 are displayed as backbone only and are not included in the provided model. In states D and E, the position of ES31 (gold, semi-transparent, backbone only) is indicated based on connectivity to helix H79, but not observed in the respective maps because of flexibility.

(C and D) Structure of the “foot” in states E (C) and F (D). In state F, Nop53 takes the place of Erb1, resulting in a conformational change in the N terminus of Rlp7.

The molecular interpretation of state F is based on the Arx1/Nog2 particle model (PDB: 3JCT) (Wu et al., 2016).