L25 functions as a conserved ribosomal docking site shared by nascent chain-associated complex and signal-recognition particle |
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Authors: | Grallath Silke Schwarz Juliane P Böttcher Ulrike M K Bracher Andreas Hartl F Ulrich Siegers Katja |
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Affiliation: | Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany. |
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Abstract: | The nascent chain-associated complex (NAC) is a dimeric protein complex of archaea and eukarya that interacts with ribosomes and translating polypeptide chains. We show that, in yeast, NAC and the signal-recognition particle (SRP) share the universally conserved ribosomal protein L25 as a docking site, which is in close proximity to the ribosomal exit tunnel. The amino-terminal segment of beta-NAC was found to be required for L25 binding. Purified NAC can prevent protein aggregation in vitro and thus shows certain properties of a molecular chaperone. Interestingly, the alpha-subunit of NAC interacts with the 54 kDa subunit of SRP. Consistent with a regulatory role of NAC in protein translocation into the endoplasmic reticulum (ER), we find that deletion of NAC results in an induction of the ER stress-response pathway. These results identify L25 as a conserved interaction platform for specific cytosolic factors that guide nascent polypeptides to their proper cellular destination. |
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