Professor Sabine Rospert, Uni Freiburg:

The Hsp70 homolog Ssb affects ribosome biogenesis via the TORC1-Sch9 signaling pathway

Friday 21. October, 10.15 N.B., N-terminalen

Abstract
Yeast cells lacking the Hsp70 chaperone Ssb suffer from severe defects in ribosome biogenesis, however, at present the mechanistic role of Ssb in this process is not understood. Our recent findings indicate that, unexpectedly, the major function of Ssb in ribosome biogenesis is not achieved by its ability to act as a folding chaperone, but rather Ssb is essential for the proper posttranslational modification of the protein kinase Sch9, which is a major positive effector of ribosome biogenesis. Specifically, Ssb is required for the proper activation of Sch9 by the TORC1-dependent phosphorylation of specific residues within the Sch9 C-terminus. Our data provide a conclusive explanation for the reduced ribosome content and the previously reported ribosome assembly defects of yeast cells lacking Ssb.