Mechanochemical Removal of Ribosome Biogenesis Factors from Nascent 60S Ribosomal Subunits

Abstract

The dynein-related AAA ATPase Rea1 is a preribosomal factor that triggers an unknown maturation step in 60S subunit biogenesis. Using electron microscopy, we show that Rea1's motor domain is docked to the pre-60S particle and its tail-like structure, harboring a metal ion-dependent adhesion site (MIDAS), protrudes from the preribosome. Typically, integrins utilize a MIDAS to bind extracellular ligands, an interaction that is strengthened under applied tensile force. Likewise, the Rea1 MIDAS binds the preribosomal factor Rsa4, which is located on the pre-60S subunit at a site that is contacted by the flexible Rea1 tail. The MIDAS-Rsa4 interaction is essential for ATP-dependent dissociation of a group of non-ribosomal factors from the pre-60S particle. Thus, Rea1 aligns with its interacting partners on the preribosome to effect a necessary step on the path to the export-competent 60S subunit.

A Puzzle of Life: Crafting Ribosomal Subunits

“…This phase is also marked by the association of the Rix1 subcomplex and the AAA-ATPase Rea1 [21,33,99] (Figures 2N and 5). Interestingly, the interaction between Rix1 and Rea1 may be regulated, as indicated by a recent study with the orthologous human proteins showing that their association is controlled by a dynamic SUMO conjugation/deconjugation cycle [100].…”

“…Subsequently, the purification of additional preribosomal particles provided a detailed spatiotemporal picture of the preribosomal intermediates and their composition [5,9,14] (Figure 2). A few of these preribosomal particles were visualized at relatively low resolution by EM [21][22][23][24]. Recent progress in cryo-EM has enabled a quantum jump by permitting the visualization of preribosomal particles at atomic or near-atomic resolution [25][26][27][28][29][30][31][32][33].…”

“…Most notably, recruitment of the gigantic Rix1-Rea1 machinery coincides with the release of Rpf2-Rrs1 and rotation of the 5S RNP into its mature position [33] (Figure 5). Once properly positioned the ATPase activity of Rea1 powers the removal of Rsa4 [21], an event that occurs The nucle(ol)ar Nog2-purified pre-60S particle contains the characteristic 'foot' structure [internal transcribed spacer 2 (ITS2) in orange] and the 5S ribonucleoprotein particle (RNP) is in its pre-mature conformation (left). During the next maturation steps, the exonucleolytic degradation of the ITS2 is coupled with the removal of the foot structure.…”

Ribosome biogenesis dysfunction leads to p53-mediated apoptosis and goblet cell differentiation of mouse intestinal stem/progenitor cells

“…Nle acts in large ribosomal subunit in yeasts, 20,21 fungi, 36 plants 37 and mammals. 23 Contrary to Drosophila, 38 Nle loss of function does not seem to interfere with the Notch pathway in the mouse hematopoietic 23 and intestinal (this study) lineages.…”

“…Its ortholog in yeast, Rsa4, was shown to be essential for the late step of maturation and subsequent export of the 60S particle. [20][21][22] We recently showed that Nle role in the maturation of the large ribosomal subunit is conserved in mouse and that Nle is required for the maintenance of hematopoietic stem cells. 23 During the course of this study, we noticed that the gut was also sensitive to Nle deletion.…”