Human RioK3 is a novel component of cytoplasmic pre-40S pre-ribosomal particles

Centre National de la Recherche Scientifique
RNA biology (Impact Factor: 4.97). 02/2012; 9(2):162-74. DOI: 10.4161/rna.18810
Source: PubMed


Maturation of the 40S ribosomal subunit precursors in mammals mobilizes several non-ribosomal proteins, including the atypical protein kinase RioK2. Here, we have investigated the involvement of another member of the RIO kinase family, RioK3, in human ribosome biogenesis. RioK3 is a cytoplasmic protein that does not seem to shuttle between nucleus and cytoplasm via a Crm1-dependent mechanism as does RioK2 and which sediments with cytoplasmic 40S ribosomal particles in a sucrose gradient. When the small ribosomal subunit biogenesis is impaired by depletion of either rpS15, rpS19 or RioK2, a concomitant decrease in the amount of RioK3 is observed. Surprisingly, we observed a dramatic and specific increase in the levels of RioK3 when the biogenesis of the large ribosomal subunit is impaired. A fraction of RioK3 is associated with the non ribosomal pre-40S particle components hLtv1 and hEnp1 as well as with the 18S-E pre-rRNA indicating that it belongs to a bona fide cytoplasmic pre-40S particle. Finally, RioK3 depletion leads to an increase in the levels of the 21S rRNA precursor in the 18S rRNA production pathway. Altogether, our results strongly suggest that RioK3 is a novel cytoplasmic component of pre-40S pre-ribosomal particle(s) in human cells, required for normal processing of the 21S pre-rRNA.

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Available from: Michèle Caizergues-Ferrer
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    • "Among the enzymes that support ribosomal subunit maturation are protein kinases. Recent data demonstrate that the human protein kinases RIO1, RIO2 and RIO3 are components of pre-40S particles and are required for their cytoplasmic maturation (Rouquette et al., 2005; Zemp et al., 2009; Baumas et al., 2012; Widmann et al., 2012). Although phosphorylation substrates for RIO kinases have not been found, recycling of certain 40S transacting factors and pre-rRNA processing are dependent on the kinase/ATPase activity of the RIO kinases (Zemp et al., 2009; Widmann et al., 2012). "
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    ABSTRACT: Biogenesis of 40S pre-ribosomal subunits requires many trans-acting factors, among them several protein kinases. In this study we show that the human CK1 isoforms δ and ε are required for cytoplasmic maturation steps of 40S subunit precursors. We show that both CK1 δ and ε isoforms are components of pre-40S subunits, where they phosphorylate the ribosome biogenesis factors ENP1/BYSL and LTV1. CK1 inhibition or co-depletion of CK1δ and ε result in failure to recycle a series of trans-acting factors including ENP1/BYSL, LTV1, RRP12, DIM2/PNO1, RIO2 and NOB1 from pre-40S particles after nuclear export. Further, CK1δ/ε co-depletion leads to defects in 18S-E pre-rRNA processing. Together, these data demonstrate that CK1δ and ε play a decisive role in triggering late steps of pre-40S maturation that are required for acquisition of functionality of 40S ribosomal subunits in protein translation.
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    • "Baumas (LBME), who identified RioK3 as a new member of the RIO kinase family involved in rRNA 18S production. She showed that RioK3 is associated in the cytoplasm with pre- 40S particles and seems to display a cytoplasmic function required for correct maturation of the 21S pre-rRNA (Baumas et al., 2012). "

    Full-text · Article · May 2012 · Research in Microbiology
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