The Hsp40 chaperone Jjj1 is required for the nucleo-cytoplasmic recycling of preribosomal factors in Saccharomyces cerevisiae

Défenses Antivirales et Antitumorales, CNRS-UMR5235, Université Montpellier II, France.
RNA (Impact Factor: 4.94). 10/2007; 13(9):1570-81. DOI: 10.1261/rna.585007
Source: PubMed


Ribosome biogenesis is a major conserved cellular pathway that requires both ribosomal proteins and many preribosomal factors. Most of the pre-60S factors are recycled into the nucleus; some of them shuttle between the nucleus and the cytoplasm while a few others, like Rei1, are strictly cytoplasmic and are mostly involved in the dissociation/recycling of the pre-60S shuttling factors. Here, we investigated the role of the Jjj1 Hsp40 chaperone in ribosome biogenesis. The absence of Jjj1 leads to a cold sensitive phenotype, a defect in the relative amount of the large ribosomal subunit with the appearance of halfmers, and to cytoplasmic accumulation of shuttling factors such as Arx1 and Alb1, which stay bound to the pre-60S particles. Jjj1 is, thus, a novel pre-60S factor involved in the last cytoplasmic steps of the large ribosomal subunit biogenesis. We report the biochemical association of Jjj1 and Rei1 to similar pre-60S complexes, their two-hybrid interactions, and their functional links. Altogether, these results indicate that Rei1 and Jjj1 share many common features. However, while the functions of Jjj1 and Rei1 partially overlap, we could distinguish specific role of the two proteins in Arx1/Alb1 and Tif6 recycling. We propose that Jjj1 is preferentially required for the release of Arx1 and Alb1 shuttling factors from the cytoplasmic pre-60S particles while Rei1 is preferentially involved in their recycling.

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Available from: Emilie Demoinet, Jan 05, 2015
    • "Mutations in Rei1 and Jjj1 lead to accumulation of Arx1 on pre-60S subunits in the cytosol (Hung and Johnson, 2006; Lo et al., 2010; Meyer et al., 2007, 2010) and block downstream pre-60S maturation events, including the release of the anti-association factor Tif6p (the yeast homolog of human eIF6) from the interface side of the 60S subunit (Lebreton et al., 2006; Lo et al., 2010). These defects can be alleviated by deletion of Arx1 (Hung and Johnson, 2006; Lebreton et al., 2006; Lo et al., 2010) or Alb1 (Demoinet et al., 2007; Lebreton et al., 2006; Meyer et al., 2007), a small, highly positively charged protein that forms a stable complex with Arx1 and is thereby recruited to the maturing pre-60S particle in the nucleoplasm (Bradatsch et al., 2007, 2012; Lebreton et al., 2006). These observations indicate that events at the tunnel exit are coordinated with maturation steps at the subunit interface and that the presence of Arx1 and Alb1 is inhibitory to downstream maturation. "
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    • "Rpl24Ap or the almost-identical Rpl24Bp are thought to replace Rlp24p in the cytosol. Jjj1p is an Hsp40 heat shock chaperone (Demoinet et al., 2007) and cooperates with Rei1p to remove Alb1p from the pre-60S subunit (Meyer et al., 2010). This step initiates Arx1p and Alb1p recycling to the nucleus. "
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    • "The cytosol/nucleus of the budding yeast, S. cerevisiae, which contains a large functional network of 13 J-protein superfamily members, has been useful as a model system for understanding the diversity of J-protein function in cellular processes. This has particularly been the case for J-proteins structurally different from those of the DnaJ-type, such as Cwc23 (Sahi et al. 2010) and Jjj1 (Demoinet et al. 2007; Meyer et al. 2007), which are involved in mRNA splicing and ribosome biogenesis, respectively. The abundant DnaJ-type J-protein of the cytosol/nucleus, Ydj1, has also been studied extensively and shown to play general roles in de novo protein folding, protein translocation across membranes , and thermotolerance (Becker et al. 1996; Glover and Lindquist 1998; Summers et al. 2009). "
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