title: The specialized cytosolic J-protein, Jjj1, functions in 60S ribosomal subunit biogenesis.
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.
authors.affiliation: Department of Biochemistry, 433 Babcock Drive, University of Wisconsin, Madison, WI 53706, USA.
authors.forename: Alison E
authors.initials: AE
authors.lastname: Meyer
authors.forename: Nai-Jung
authors.initials: NJ
authors.lastname: Hung
authors.forename: Peizhen
authors.initials: P
authors.lastname: Yang
authors.forename: Arlen W
authors.initials: AW
authors.lastname: Johnson
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Craig
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D015966:Gene Expression Regulation, Fungal; D050956:HSP40 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D018832:Molecular Chaperones; D010641:Phenotype; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012270:Ribosomes / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D013696:Temperature
chemical_list: D004268:DNA-Binding Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; C517792:Jjj1 protein, S cerevisiae; D018832:Molecular Chaperones; C511835:REI1 protein, S cerevisiae; C095192:SSB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C077019:ZUO1 protein, S cerevisiae; D000251:Adenosine Triphosphatases; C095973:SSA1 protein, S cerevisiae