title: A functional chaperone triad on the yeast ribosome.
abstract: The chaperones RAC (ribosome-associated complex), consisting of Ssz1p and zuotin, and Ssb1/2p are associated with ribosomes of yeast. Ssb1/2p was previously shown to form a crosslink product to polypeptides trapped in ribosome-nascent chain complexes (RNCs) in vitro. Here we show that an efficient crosslink of the nascent chain to Ssb1/2p depends on the presence of functional RAC. The crosslink to Ssb1/2p was significantly diminished if (i) RAC was removed from RNCs: a process reversed by addition of purified RAC; (ii) RAC carried a mutation in the J-domain of zuotin, leading to its inactivation in vivo; (iii) RAC's Ssz1p subunit was absent because RNCs were generated in a Deltassz1-derived translation extract. In vivo the same specific set of growth defects caused by the absence of any of the three chaperones was also displayed by a Deltassb1/2Deltassz1Deltazuo1 strain. The combination of in vitro and in vivo data supports a model in which Ssb1/2p, Ssz1p, and zuotin act in concert on nascent chains while they are being synthesized.
authors.affiliation: Max-Planck Research Unit Enzymology of Protein Folding, Weinbergweg 22, D-06120 Halle, Saale, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Gautschi
authors.forename: Andrej
authors.initials: A
authors.lastname: Mun
authors.forename: Suzanne
authors.initials: S
authors.lastname: Ross
authors.forename: Sabine
authors.initials: S
authors.lastname: Rospert
mesh_terms: D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D005656:Fungal Proteins / Q000737:chemistry / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins / Q000737:chemistry / Q000502:physiology*; D018832:Molecular Chaperones / Q000502:physiology*; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; C095192:SSB1 protein, S cerevisiae; C101143:SSB2 protein, S pombe; C424445:SSZ1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C077019:ZUO1 protein, S cerevisiae