The CryoEM structure of the Saccharomyces cerevisiae ribosome maturation factor Rea1.

Piotr Sosnowski,Andreas Boland,Johan Busselez,Linas Urnavicius,Gabor Papai,Helgo Schmidt,Robert Fagiewicz

doi:10.7554/elife.39163

Abstract

The biogenesis of 60S ribosomal subunits is initiated in the nucleus where rRNAs and proteins form pre-60S particles. These pre-60S particles mature by transiently interacting with various assembly factors. The ~5000 amino-acid AAA+ ATPase Rea1 (or Midasin) generates force to mechanically remove assembly factors from pre-60S particles, which promotes their export to the cytosol. Here we present three Rea1 cryoEM structures. We visualise the Rea1 engine, a hexameric ring of AAA+ domains, and identify an α-helical bundle of AAA2 as a major ATPase activity regulator. The α-helical bundle interferes with nucleotide-induced conformational changes that create a docking site for the substrate binding MIDAS domain on the AAA +ring. Furthermore, we reveal the architecture of the Rea1 linker, which is involved in force generation and extends from the AAA+ ring. The data presented here provide insights into the mechanism of one of the most complex ribosome maturation factors.

Highlights

Eukaryotic ribosome assembly is tightly controlled by more than 200 assembly factors to ensure faithful protein synthesis (Thomson et al, 2013)
During the initial stages of ribosome biogenesis, rRNAs, ribosomal proteins, and assembly factors associate into nucleolar pre-60S particles, which mature into functional large ribosomal subunits in the cytosol (Kressler et al, 2010)
The most prominent feature of the Rea1 AAA+ ring is the AAA2L-H2a insert that sits like a plug in the central pore of the AAA+ ring

Summary

Introduction

Eukaryotic ribosome assembly is tightly controlled by more than 200 assembly factors to ensure faithful protein synthesis (Thomson et al, 2013). During the initial stages of ribosome biogenesis, rRNAs, ribosomal proteins, and assembly factors associate into nucleolar pre-60S particles, which mature into functional large ribosomal subunits in the cytosol (Kressler et al, 2010). The AAA+ (ATPases Associated with various cellular Activities) family member Rea (or Midasin) consists of nearly 5000 amino acids and generates force to mechanically remove assembly factors. Rea removes the assembly factor Rsa (Ulbrich et al, 2009), which triggers a signalling pathway that recruits RanGTP to pre-60S particles to export them to the cytosol (Ulbrich et al, 2009; Matsuo et al, 2014) (Figure 1A). Despite its crucial importance for pre-60S particle maturation, the Rea structure and mechanism have remained largely enigmatic

Methods

Results

Conclusion