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EMBO reports 7, 1, 78–84 (2006)
doi:10.1038/sj.embor.7400551
Published online: 14 October 2005
L25 functions as a conserved ribosomal docking site shared by nascent chain-associated complex and signal-recognition particle
Silke Grallath1, 2, Juliane P Schwarz1, 2, Ulrike M K Böttcher1, Andreas Bracher1, F Ulrich Hartl1 & Katja Siegers1, 2
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1 Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried 82152, Germany
2 These authors contributed equally to this work
To whom correspondence should be addressed
Katja Siegers Tel: +49 89 8578 2295; Fax: +49 89 8578 2211; E-mail: siegers@biochem.mpg.de
Received 14 July 2005; Accepted 13 September 2005; Published online 14 October 2005.
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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  -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  -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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