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A functional chaperone triad on the yeast ribosome

2002; National Academy of Sciences; Volume: 99; Issue: 7 Linguagem: Inglês

10.1073/pnas.062048599

1091-6490

Matthias Gautschi, Andrej Mun, Suzanne Ross, Sabine Rospert,

RNA modifications and cancer

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 Δ ssz1 -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 Δ ssb1 / 2 Δ ssz1 Δ zuo1 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.