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Journal of Bacteriology, October 2001, p. 5911-5917, Vol. 183, No. 20
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.20.5911-5917.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

The C Terminus of sigma 32 Is Not Essential for Degradation by FtsH

Toshifumi Tomoyasu,1,dagger Florence Arsène,1,Dagger Teru Ogura,2 and Bernd Bukau1,*

Institut für Biochemie und Molekularbiologie, Universität Freiburg, D-79104 Freiburg, Germany,1 and Division of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, Kuhonji 4-24-1, Kumamoto 862-0976, Japan2

Received 23 April 2001/Accepted 21 June 2001

A key step in the regulation of heat shock genes in Escherichia coli is the stress-dependent degradation of the heat shock promoter-specific sigma 32 subunit of RNA polymerase by the AAA protease, FtsH. Previous studies implicated the C termini of protein substrates, including sigma 32, as degradation signals for AAA proteases. We investigated the role of the C terminus of sigma 32 in FtsH-dependent degradation by analysis of C-terminally truncated sigma 32 mutant proteins. Deletion of the 5, 11, 15, and 21 C-terminal residues of sigma 32 did not affect degradation in vivo or in vitro. Furthermore, a peptide comprising the C-terminal 21 residues of sigma 32 was not degraded by FtsH in vitro and thus did not serve as a recognition sequence for the protease, while an unrelated peptide of similar length was efficiently degraded. The truncated sigma 32 mutant proteins remained capable of associating with DnaK and DnaJ in vitro but showed intermediate (5-amino-acid deletion) and strong (11-, 15-, and 21-amino-acid deletions) defects in association with RNA polymerase in vitro and biological activity in vivo. These results indicate an important role for the C terminus of sigma 32 in RNA polymerase binding but no essential role for FtsH-dependent degradation and association of chaperones.

* Corresponding author. Mailing address: Institut für Biochemie und Molekularbiologie, Universität Freiburg, Hermann-Herder Str. 7, D-79104 Freiburg, Germany. Phone: 49-761 203 52 22. Fax: 49-761 203 52 57. E-mail: bukau{at}ruf.uni-freiburg.de.

dagger Present address: Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, Inageku, Chiba 263-8522, Japan.

Dagger Present address: Laboratoire de Microbiologie et de Génétique, Université Louis Pasteur, CNRS UPRES A7010, 28 67083 Strasbourg Cedex, France.

Journal of Bacteriology, October 2001, p. 5911-5917, Vol. 183, No. 20
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.20.5911-5917.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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Copyright © 2001 by the American Society for Microbiology. All rights reserved.