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
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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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    ABSTRACT: The evolutionarily conserved proteins REIL1 and REIL2 (for REI1-LIKE) have four conserved zinc finger domains and are A. thaliana homologs of the cytosolic 60S ribosomal maturation factor Rei1p from yeast and its paralog Reh1p. The yeast and A. thaliana paralogs result from independent gene duplications. The A. thaliana REIL paralogs are required specifically in the cold (10°C) but not for growth at optimal temperature (20°C). A reil1-1 reil2-1 double mutant is arrested at 10°C prior to the emergence of the first rosette leaf. Two allelic reil2 mutants, reil2-1 and reil2-2, form small spoon-shaped leafs at 10°C. This phenomenon reverts after emergence of the inflorescence in the cold or upon shift to 20°C. Except for a slightly delayed germination, a reil1-1 mutant shows no further growth phenotype under the currently investigated conditions. A comparative analysis demonstrates conserved co-expression of orthologous genes from yeast and A. thaliana that are co-regulated with yeast rei1 or with A. thaliana REIL2, respectively. The conserved correlations point to a role of A. thaliana REIL proteins in the maturation of the eukaryotic ribosomal 60S subunit. We support this conclusion by heterologous complementation of the cold induced growth defect of the yeast Δrei1 deletion.
    Plant physiology 09/2013; 163(4). DOI:10.1104/pp.113.223925 · 6.84 Impact Factor
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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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    ABSTRACT: Across eukaryotes, Hsp70-based chaperone machineries display an underlying unity in their sequence, structure and biochemical mechanism of action, while working in a myriad of cellular processes. In good part, this extraordinary functional versatility is derived from the ability of a single Hsp70 to interact with an array of J-protein co-chaperones to form a functional chaperone network. Among J-proteins, the DnaJ-type is the most prevalent, being present in all three kingdoms and in several different compartments of eukaryotic cells. However, because these ancient DnaJ-type proteins diverged at the base of the eukaryotic phylogeny, little is understood about the evolutionary basis of their diversification and thus the functional expansion of the chaperone network. Here we report results of evolutionary and experimental analyses of two more recent members of the cytosolic DnaJ family of Saccharomyces cerevisiae, Xdj1 and Apj1, which emerged by sequential duplications of the ancient YDJ1 in Ascomycota. Sequence comparison and molecular modeling revealed that both Xdj1 and Apj1 maintained a domain organization similar to that of multifunctional Ydj1. However despite these similarities, both Xdj1 and Apj1 evolved highly specialized functions. Xdj1 plays a unique role in the translocation of proteins from the cytosol into mitochondria. Apj1's specialized role is related to degradation of sumolyated proteins. Together these data provide the first clear example of co-chaperone duplicates that evolved specialized functions, allowing expansion of the chaperone functional network, while maintaining the overall structural organization of their parental gene.
    Molecular Biology and Evolution 01/2013; 30(5). DOI:10.1093/molbev/mst008 · 9.11 Impact Factor
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    • "However, we also found that Tif6 mislocalized in jjj1D cells (Figure 6A). The weaker mislocalization of Tif6-GFP in jjj1D compared to rei1D cells is consistent with milder growth defect of a jjj1D mutant compared to an rei1D mutant (Demoinet et al., 2007; Meyer et al., 2007). Nevertheless , the common effect on Tif6 localization implies that Rei1 and Jjj1 both act upstream of Tif6 release. "
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    ABSTRACT: In eukaryotic cells the final maturation of ribosomes occurs in the cytoplasm, where trans-acting factors are removed and critical ribosomal proteins are added for functionality. Here, we have carried out a comprehensive analysis of cytoplasmic maturation, ordering the known steps into a coherent pathway. Maturation is initiated by the ATPase Drg1. Downstream, assembly of the ribosome stalk is essential for the release of Tif6. The stalk recruits GTPases during translation. Because the GTPase Efl1, which is required for the release of Tif6, resembles the translation elongation factor eEF2, we suggest that assembly of the stalk recruits Efl1, triggering a step in 60S biogenesis that mimics aspects of translocation. Efl1 could thereby provide a mechanism to functionally check the nascent subunit. Finally, the release of Tif6 is a prerequisite for the release of the nuclear export adaptor Nmd3. Establishing this pathway provides an important conceptual framework for understanding ribosome maturation.
    Molecular cell 07/2010; 39(2):196-208. DOI:10.1016/j.molcel.2010.06.018 · 14.02 Impact Factor
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