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Journal of Bacteriology, July 2008, p. 5120-5126, Vol. 190, No. 14
0021-9193/08/$08.00+0     doi:10.1128/JB.00012-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Membrane-Bound Transcriptional Regulator CadC Is Activated by Proteolytic Cleavage in Response to Acid Stress

School of Life Sciences and Biotechnology, Korea University, Seoul 136-701,¹ Department of Microbiology and Immunology, Chosun University School of Dentistry, Gwangju 501-759, South Korea²

Received 4 January 2008/ Accepted 7 May 2008

Proteolytic processes often participate in signal transduction across bacterial membranes. In Salmonella enterica serovar Typhimurium, the transcriptional regulator CadC activates genes of lysine decarboxylase system in response to external acidification and exogenous lysine. However, the signaling mechanism of CadC activation remains unexplored. We report here that CadC is located on the inner membrane under normal growth conditions but rapidly cleaved under acid stress conditions, leading to the induction of target gene transcription. As full-length CadC is degraded, the N-terminal fragment containing the DNA-binding domain accumulates in the inner membrane. Moreover, we show that C-terminal truncations of CadC abolish its degradation, resulting in complete loss of activator function. Together, these observations suggest that site-specific proteolysis at the periplasmic domain of CadC generates a biologically active form of N-terminal DNA-binding domain to promote target gene activation.

Published ahead of print on 16 May 2008.