The proposed pathway for binding and release of Bud23 from 40S precursors. A pathway based on structures from yeast and human 40S biogenesis intermediates is shown to visualize the stage-specific association of Bud23 with the pre-40S intermediates. Each intermediate is shown from the intersubunit and the solvent views. The final metastable intermediate of processome disassembly, Dis-C (PDB 6ZQG), contains multiple Processome factors, including the U3 snoRNA, Dhr1, Bms1, Enp1, and Pno1 (Cheng et al. 2020). The binding of Bud23, and its partner Trm112, to Dis-C promotes its transformation into the pre-40S (Black et al. 2020). This transition comes with the release of most Processome factors and yields the earliest pre-40S intermediate, State A (PDB 6G4W) (Ameismeier et al. 2018). During this transition, Tsr1 and Ltv1 also are observed on the pre-40S. Rrp12, which is resolved in earlier Processome intermediates (Singh et al. 2021) but is not in Dis-C, is also seen in State A. Between State A to State B (PDB 6G4S), Nob1, more of Ltv1, and the Rps0-cluster proteins become resolved, and Bud23 and Trm112 are no longer observed. Rrp12 and the rRNA near it also undergo structural remodeling during this transition. Between State B and State C (PDB 6G18), Rio2 and several RPs become resolved while Rrp12 appears to be released. Molecular visualization was generated in UCSF ChimeraX v0.93 (Goddard et al. 2018).
