Structural and functional analysis of Utp24, an endonuclease for processing 18S ribosomal RNA.

Weidong An,Keqiong Ye,Yifei Du,Katrin Karbstein

doi:10.1371/journal.pone.0195723

Weidong An, Keqiong Ye + Show 2 more

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https://doi.org/10.1371/journal.pone.0195723

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Abstract

The precursor ribosomal RNA is processed by multiple steps of nucleolytic cleavage to generate mature rRNAs. Utp24 is a PIN domain endonuclease in the early 90S precursor of small ribosomal subunit and is proposed to cleave at sites A1 and A2 of pre-rRNA. Here we determine the crystal structure of Utp24 from Schizosaccharomyces pombe at 2.1 angstrom resolution. Utp24 structurally resembles the ribosome assembly factor Utp23 and both contain a Zn-finger motif. Functional analysis in Saccharomyces cerevisiae shows that depletion of Utp24 disturbs the assembly of 90S and abolishes cleavage at sites A0, A1 and A2. The 90S assembled with inactivated Utp24 is arrested at a post-A0-cleavage state and contains enriched nuclear exosome for degradation of 5' ETS. Despite of high sequence conservation, Utp24 from other organisms is unable to form an active 90S in S. cerevisiae, suggesting that Utp24 needs to be precisely positioned in 90S. Our study provides biochemical and structural insight into the role of Utp24 in 90S assembly and activity.

Highlights

Of yeast ribosome requires processing and modification of rRNAs and association of 79 ribosomal proteins [1, 2]
Processing of 18S rRNA occurs in the nucleolus within the 90S pre-ribosome or the small subunit processome [4, 5], which is the early assembly intermediate of small ribosomal subunits
The full-length protein of spUtp24 was used in crystallization, the crystal structure contains only the PIN domain

Summary

Introduction

Of yeast ribosome requires processing and modification of rRNAs and association of 79 ribosomal proteins [1, 2]. This process begins with the transcription of a 35S precursor rRNA (pre-rRNA) that encodes 18S, 5.8S and 25S rRNAs and the external (5’ ETS and 3’ ETS) and internal (ITS1 and ITS2) transcribed spacers. The 90S pre-ribosome is co-transcriptionally assembled from ~70 non-ribosomal assembly factors (AFs), U3, U14, snR30 and snR10 snoRNAs and ~ 20 ribosomal proteins in a stepwise and dynamic manner [6,7,8]. At the final stage of 90S formation, the U14 and snR30 snoRNAs and a dozen labile AFs recruited by the 18S region are released, resulting in a fully

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