The specialized cytosolic J-protein, Jjj1, functions in 60S ribosomal subunit biogenesis

Department of Biochemistry, 433 Babcock Drive, University of Wisconsin, Madison, WI 53706, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 02/2007; 104(5):1558-63. DOI: 10.1073/pnas.0610704104
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ABSTRACT J-proteins and Hsp70 chaperones function together in diverse cellular processes. We identified a cytosolic J-protein, Jjj1, of Saccharomyces cerevisiae that is associated with 60S ribosomal particles. Unlike Zuo1, a 60S subunit-associated J-protein that is a component of the chaperone machinery that binds nascent polypeptide chains upon their exit from the ribosome, Jjj1 plays a role in ribosome biogenesis. Cells lacking Jjj1 have phenotypes very similar to those lacking Rei1, a ribosome biogenesis factor associated with pre-60S ribosomal particles in the cytosol. Jjj1 stimulated the ATPase activity of the general cytosolic Hsp70 Ssa, but not Ssb, Zuo1's ribosome-associated Hsp70 partner. Overexpression of Jjj1, which is normally approximately 40-fold less abundant than Zuo1, can partially rescue the phenotypes of cells lacking Zuo1 as well as cells lacking Ssb. Together, these results are consistent with the idea that Jjj1 normally functions with Ssa in a late, cytosolic step of the biogenesis of 60S ribosomal subunits. In addition, because of its ability to bind 60S subunits, we hypothesize that Jjj1, when overexpressed, is able to partially substitute for the Zuo1:Ssb chaperone machinery by recruiting Ssa to the ribosome, facilitating its interaction with nascent polypeptide chains.

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Available from: Arlen Johnson, Jan 13, 2014
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    • "Although the role of TORC1 in phosphorylation of ribosomal protein S6 (RPS6) via S6-kinase (S6K) is known (Feldman et al., 2009; Richardson et al., 2004; Urban et al., 2007), the involvement of TORC2 was not appreciated until recently (Zinzalla et al., 2011). Our data support a role of TORC2 in ribosome biogenesis, since two genes (TMA23 and JJJ1) involved in ribosome biogenesis (Fleischer et al., 2006; Meyer et al., 2007) and a ribosomal protein (RPL37A) show strong positive interactions with TORC2 while simultaneously showing strong negative interactions with TORC1 (Figure 2G). This indicates that these genes are in a pathway with TORC2 and provides additional evidence that ribosomal biogenesis plays a role in regulating TORC2 (Zinzalla et al., 2011). "
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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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