Abstract
Eukaryotic ribosomes are synthesized in a hierarchical process driven by a plethora of assembly factors, but how maturation events at physically distant sites on pre-ribosomes are coordinated is poorly understood. Using functional analyses and cryo-EM, we show that ribosomal protein Rps20 orchestrates communication between two multi-step maturation events across the pre-40S subunit. Our study reveals that during pre-40S maturation, formation of essential contacts between Rps20 and Rps3 permits assembly factor Ltv1 to recruit the Hrr25 kinase, thereby promoting Ltv1 phosphorylation. In parallel, a deeply buried Rps20 loop reaches to the opposite pre-40S side, where it stimulates Rio2 ATPase activity. Both cascades converge to the final maturation steps releasing Rio2 and phosphorylated Ltv1. We propose that conformational proofreading exerted via Rps20 constitutes a checkpoint permitting assembly factor release and progression of pre-40S maturation only after completion of all earlier maturation steps.
Highlights
Eukaryotic ribosomes are synthesized in a hierarchical process driven by a plethora of assembly factors, but how maturation events at physically distant sites on pre-ribosomes are coordinated is poorly understood
The synthesis of ribosomes is a highly complex process starting with the assembly of prerRNA, r-proteins, and ribosome assembly factors (AFs) into preribosomal particles in the nucleolus
We suggest that sensing of the correct conformations of both maturation sites, exerted by Rps[20], provides a quality control checkpoint, which ensures that release of Ltv[1] and Rio[2] is only triggered once all necessary earlier maturation steps have been completed
Summary
Eukaryotic ribosomes are synthesized in a hierarchical process driven by a plethora of assembly factors, but how maturation events at physically distant sites on pre-ribosomes are coordinated is poorly understood. Several biochemical studies together with recent cryo-electron microscopy (cryo-EM) structural analyses provided insights into the organization of early cytoplasmic pre-40S particles, revealing that AFs Tsr[1], Pno[1], Nob[1], Dim[1], and Rio[2] are located on the intersubunit side of the pre-40S subunit and that Enp[1] and Ltv[1] are bound on the solvent-exposed side in the area of the beak structure[10,14,15,16,17,18,19,20,21,22] These early cytoplasmic pre-40S particles undergo a cascade of maturation events, with the two first and presumably rate limiting ones being two different ATPdependent maturation steps, resulting in dissociation of AFs Rio[2] and Ltv[114,19,23,24,25,26]. Not known whether these two steps are interconnected and in which order they occur
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
