Good Vibrations: Structural Remodeling of Maturing Yeast Pre-40S Ribosomal Particles Followed by Cryo-Electron Microscopy.

Ramtin Shayan,Pierre-Emmanuel Gleizes,Natacha Larburu,Laura Plassart,Célia Plisson-Chastang,Simon Lebaron,Stéphanie Balor,David Bouyssié,Dana Rinaldi,Julien Marcoux

doi:10.3390/molecules25051125

Abstract

Assembly of eukaryotic ribosomal subunits is a very complex and sequential process that starts in the nucleolus and finishes in the cytoplasm with the formation of functional ribosomes. Over the past few years, characterization of the many molecular events underlying eukaryotic ribosome biogenesis has been drastically improved by the “resolution revolution” of cryo-electron microscopy (cryo-EM). However, if very early maturation events have been well characterized for both yeast ribosomal subunits, little is known regarding the final maturation steps occurring to the small (40S) ribosomal subunit. To try to bridge this gap, we have used proteomics together with cryo-EM and single particle analysis to characterize yeast pre-40S particles containing the ribosome biogenesis factor Tsr1. Our analyses lead us to refine the timing of the early pre-40S particle maturation steps. Furthermore, we suggest that after an early and structurally stable stage, the beak and platform domains of pre-40S particles enter a “vibrating” or “wriggling” stage, that might be involved in the final maturation of 18S rRNA as well as the fitting of late ribosomal proteins into their mature position.

Highlights

In every living cells, ribosomes are RNP particles that translate genomic information into proteins.These huge molecular machines are composed of a small and a large subunit, carrying the decoding center and peptidyl transferase activity, respectively
Transmission electron microscopy (TEM) observations after negative staining confirmed that the particles sedimenting on lighter fractions had the overall size and shape of 40S subunits, while heavier fractions contained larger, rounder objects, with dimensions compatible with 80S-like particles (Figure 1a, lower panel)
Cryo-EM Structures Suggest that pre-40S Particles Transit through a Vibrating State

Summary

Introduction

Ribosomes are RNP particles that translate genomic information into proteins.These huge molecular machines are composed of a small and a large subunit, carrying the decoding center and peptidyl transferase activity, respectively. Molecules 2020, 25, 1125; doi:10.3390/molecules25051125 www.mdpi.com/journal/molecules (RBFs) These RBFs are proteins that drive pre-rRNA cleavage, modification and folding, as well as RPs chaperoning and integration into nascent ribosomal subunit precursors. They were quasi-exhaustively identified two decades ago by genetic screens or proteomics studies [1,2,3], and have been predicted to harbor various activities such as NTPase, nuclease, helicase or kinase based on their secondary structures (for reviews, [4,5,6,7]), the precise role of most RBFs in ribosome biogenesis remains elusive

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Conclusion