A functional chaperone triad on the yeast ribosome

Area of Science:

• Molecular Biology
• Protein Synthesis
• Chaperone Function

Background:

• Ribosome-associated chaperones play crucial roles in protein folding and quality control.
• The ribosome-associated complex (RAC), comprising Ssz1p and zuotin, and Ssb1/2p are yeast chaperones associated with ribosomes.
• Previous studies indicated Ssb1/2p can crosslink to nascent chains in vitro.

Purpose of the Study:

• To investigate the functional relationship between RAC and Ssb1/2p in nascent chain crosslinking.
• To determine the necessity of functional RAC for efficient Ssb1/2p-nascent chain crosslinking.
• To elucidate the in vivo roles of Ssb1/2p, Ssz1p, and zuotin in yeast.

Main Methods:

• In vitro crosslinking assays using ribosome-nascent chain complexes (RNCs).
• Manipulation of RAC and its subunits (Ssz1p, zuotin) on RNCs.
• Generation of RNCs in translation extracts lacking specific chaperone subunits.
• In vivo analysis of growth defects in yeast strains with deletions in chaperone genes.

Main Results:

• Efficient crosslinking of nascent chains to Ssb1/2p requires functional RAC.
• Removal or inactivation of RAC significantly diminishes Ssb1/2p crosslinking.
• Absence of Ssz1p within RAC also impairs Ssb1/2p crosslinking.
• In vivo, deletion of all three chaperones (Ssb1/2p, Ssz1p, zuotin) results in similar growth defects.

Conclusions:

• Ssb1/2p, Ssz1p, and zuotin function in a coordinated manner on nascent polypeptide chains.
• RAC is essential for the efficient interaction of Ssb1/2p with nascent chains during translation.
• These chaperones likely act in concert to facilitate proper protein synthesis and folding.