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Journal of Bacteriology, November 2004, p. 7474-7480, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7474-7480.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Conserved Region 2.1 of Escherichia coli Heat Shock Transcription Factor {sigma}32 Is Required for Modulating both Metabolic Stability and Transcriptional Activity

Mina Horikoshi,1 Takashi Yura,2 Sachie Tsuchimoto,1 Yoshihiro Fukumori,1 and Masaaki Kanemori1*

Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa,1 Kyoto University, Kyoto, Japan2

Received 3 April 2004/ Accepted 5 May 2004

Escherichia coli heat shock transcription factor {sigma}32 is rapidly degraded in vivo, with a half-life of about 1 min. A set of proteins that includes the DnaK chaperone team (DnaK, DnaJ, GrpE) and ATP-dependent proteases (FtsH, HslUV, etc.) are involved in degradation of {sigma}32. To gain further insight into the regulation of {sigma}32 stability, we isolated {sigma}32 mutants that were markedly stabilized. Many of the mutants had amino acid substitutions in the N-terminal half (residues 47 to 55) of region 2.1, a region highly conserved among bacterial {sigma} factors. The half-lives ranged from about 2-fold to more than 10-fold longer than that of the wild-type protein. Besides greater stability, the levels of heat shock proteins, such as DnaK and GroEL, increased in cells producing stable {sigma}32. Detailed analysis showed that some stable {sigma}32 mutants have higher transcriptional activity than the wild type. These results indicate that the N-terminal half of region 2.1 is required for modulating both metabolic stability and the activity of {sigma}32. The evidence suggests that {sigma}32 stabilization does not result from an elevated affinity for core RNA polymerase. Region 2.1 may, therefore, be involved in interactions with the proteolytic machinery, including molecular chaperones.

* Corresponding author. Mailing address: Department of Biology, Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan. Phone: 81-76-264-6229. Fax: 81-76-264-6230. E-mail: mkanemo{at}kenroku.kanazawa-u.ac.jp.

Journal of Bacteriology, November 2004, p. 7474-7480, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7474-7480.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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