Figure 6.

Proteins coimmunoprecipitated with the exosome in higher levels in the absence of Nop53 participate in different phases of ribosomal maturation. A, structural representation of 90S pre-ribosomes with the identified protein complexes are depicted in different colors as follows: pink, UTP-A; blue, UTP-B; orange, UTP-C; green, U3 snoRNP; yellow, Mpp10 complex. Proteins in bold letters are those indicated in Fig. 5B. The remaining parts of the particle are represented in light gray. B, individual proteins from the subcomplexes indicated in (A) are highlighted in different colors. C, schematics of the positions of the proteins in the 90S particle and their interactions within the particle. Note that all proteins interacting more efficiently with the exosome in the absence of Nop53 are exposed on the same face of 90S. Structure of the 90S particle was based on Ref. 37 (PDB 5WLC). D, representation of pre-60S maturation pathway, with the factors identified here highlighted in different colors. The exosome associates with various pre-60S intermediates in the absence of Nop53. Schematics show the interactions between the proteins identified here within the pre-60S. Structures of pre-60S particles were based on Refs. 25, 36. State A (PDB 6EM3), state B (PDB 6EM4), state C (PDB 6EM1), state D (PDB 6EM5), state E (PDB 6ELZ), and late nuclear states (PDB 3JCT) are shown.