Stepwise assembly of the earliest precursors of large ribosomal subunits in yeast. Issue 11 (11th April 2017)

• Record Type: Journal Article
• Authors: Chen, Wu; Xie, Zhensheng; Yang, Fuquan; Ye, Keqiong
• Is Part Of: Nucleic acids research. Volume 45:Issue 11(2017)
• Page Start: 6837
• Page End: 6847
• Publication Date: 2017-04-11
• Subjects: Nucleic acids -- Periodicals; Molecular biology -- Periodicals; 572.805
• DOI: 10.1093/nar/gkx254
• Languages: English
• ISSNs: 0305-1048

Abstract

Abstract: Small ribosomal subunits are co-transcriptionally assembled on the nascent precursor rRNA in Saccharomyces cerevisiae . It is unknown how the highly intertwined structure of 60S large ribosomal subunits is initially formed. Here, we affinity purified and analyzed a series of pre-60S particles assembled in vivo on plasmid-encoded pre-rRNA fragments of increasing lengths, revealing a spatiotemporal assembly map for 34 trans-acting assembly factors (AFs), 30 ribosomal proteins and 5S rRNA. The gradual association of AFs and ribosomal proteins with the pre-rRNA fragments strongly supports that the pre-60S is co-transcriptionally, rather than post-transcriptionally, assembled. The internal and external transcribed spacers ITS1, ITS2 and 3΄ ETS in pre-rRNA must be processed in pre-60S. We show that the processing machineries for ITS1 and ITS2 are primarily recruited by the 5΄ and 3΄ halves of pre-27S RNA, respectively. Nevertheless, processing of both ITS1 and ITS2 requires a complete 25S region. The 3΄ ETS plays a minor role in ribosome assembly, but is important for efficient rRNA processing and ribosome maturation. We also identified a distinct pre-60S state occurring before ITS2 processing. Our data reveal the elusive co-transcriptional assembly pathway of large ribosomal subunit.