Journal
EMBO REPORTS
Volume -, Issue -, Pages -Publisher
WILEY
DOI: 10.15252/embr.202357984
Keywords
5S RNP; ITS2; pre-60S ribosome; ribosome biogenesis; rixosome
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The study isolated and described the conserved rixosome from Chaetomium thermophilum, which consists of two sub-modules, Rix1-Ipi3-Ipi1 and Las1-Grc3 complex. The Rix1 complex plays a key role in pre-60S particles by inserting between the 5S rRNA tip and L1-stalk, facilitating the rotation of immature 5S RNP. The other sub-module with Las1 endonuclease and Grc3 polynucleotide-kinase cleaves and phosphorylates the nearby ITS2 pre-rRNA at the pre-60S foot. Inward movement of the L1 stalk permits the Nop53 N-terminus with AIM motif to participate in completing ITS2 removal.
The rixosome defined in Schizosaccharomyces pombe and humans performs diverse roles in pre-ribosomal RNA processing and gene silencing. Here, we isolate and describe the conserved rixosome from Chaetomium thermophilum, which consists of two sub-modules, the sphere-like Rix1-Ipi3-Ipi1 and the butterfly-like Las1-Grc3 complex, connected by a flexible linker. The Rix1 complex of the rixosome utilizes Sda1 as landing platform on nucleoplasmic pre-60S particles to wedge between the 5S rRNA tip and L1-stalk, thereby facilitating the 180(degrees) rotation of the immature 5S RNP towards its mature conformation. Upon rixosome positioning, the other sub-module with Las1 endonuclease and Grc3 polynucleotide-kinase can reach a strategic position at the pre-60S foot to cleave and 5 ' phosphorylate the nearby ITS2 pre-rRNA. Finally, inward movement of the L1 stalk permits the flexible Nop53 N-terminus with its AIM motif to become positioned at the base of the L1-stalk to facilitate Mtr4 helicase-exosome participation for completing ITS2 removal. Thus, the rixosome structure elucidates the coordination of two central ribosome biogenesis events, but its role in gene silencing may adapt similar strategies.
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