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Journal of Bacteriology, November 2009, p. 7017-7026, Vol. 191, No. 22
0021-9193/09/$08.00+0     doi:10.1128/JB.00208-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Depletion of the Signal Recognition Particle Receptor Inactivates Ribosomes in Escherichia coli{triangledown}

Jonas Bürk,1,# Benjamin Weiche,1,# Meike Wenk,1,2 Diana Boy,1,2 Sigrun Nestel,3 Bernd Heimrich,3 and Hans-Georg Koch1*

Institut für Biochemie und Molekularbiologie, ZBMZ, Stefan-Meier-Strasse 17,1 Fakultät für Biologie, Schänzlestrasse 1,2 Institut für Anatomie und Zellbiologie, Albertstrasse 17, Albert-Ludwigs Universität, 79104 Freiburg, Germany3

Received 17 February 2009/ Accepted 3 September 2009

The signal recognition particle (SRP)-dependent cotranslational targeting of proteins to the cytoplasmic membrane in bacteria or the endoplasmic reticulum membrane in eukaryotes is an essential process in most living organisms. Eukaryotic cells have been shown to respond to an impairment of the SRP pathway by (i) repressing ribosome biogenesis, resulting in decreased protein synthesis, and (ii) by increasing the expression of protein quality control mechanisms, such as chaperones and proteases. In the current study, we have analyzed how bacteria like Escherichia coli respond to a gradual depletion of FtsY, the bacterial SRP receptor. Our analyses using cell-free transcription/translation systems showed that FtsY depletion inhibits the translation of both SRP-dependent and SRP-independent proteins. This synthesis defect is the result of a multifaceted response that includes the upregulation of the ribosome-inactivating protein ribosome modulation factor (RMF). Although the consequences of these responses in E. coli are very similar to some of the effects also observed in eukaryotic cells, one striking difference is that E. coli obviously does not reduce the rate of protein synthesis by downregulating ribosome biogenesis. Instead, the upregulation of RMF leads to a direct and reversible inhibition of translation.

* Corresponding author. Mailing address: Institut für Biochemie und Molekularbiologie, ZBMZ, Albert-Ludwigs Universität Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany. Phone: 0049 761 2035250. Fax: 0049 761 2035289. E-mail: Hans-Georg.Koch{at}biochemie.uni-freiburg.de

{triangledown} Published ahead of print on 11 September 2009.

# Both authors contributed equally to this work.

Journal of Bacteriology, November 2009, p. 7017-7026, Vol. 191, No. 22
0021-9193/09/$08.00+0     doi:10.1128/JB.00208-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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