Yi-Hsuan Pan?, Chen-Chung Liao?, Chou-Chiang Kuo§, Kow-Jen Duan§, Po-Huang Liang?, Hanna S. Yuan
,Shiau-Ting Hu**, and Kin-Fu Chak?1

From the ?Institute of Biochemistry and the **Institute of Microbiology and Immunology, National Yang Ming University, Taipei 11221, the §Institute of Bioengineering, Tatung University, Taipei 10452, and the ?Institute of Biological Chemistry and Molecular Biology, Academic Sinica, Taipei 1529, Taiwan

The ColE7 operon is an SOS response regulon, which encodes bacteriocin ColE7 to kill susceptible Escherichia coli and its related enterobacteria under conditions of stress.Wehave observed for the first time that polyamines confer limited resistance against ColE7 on E. coli cells. Thus, this study aims to investigate the role of polyamines in modulating the protective effect of the E. coli cells against colicin. In the experiments, we surprisingly found that endogenous polyamines are also essential for ColE7 production, and the rate of polyamine synthesis is directly related to the SOS response. Our experimental results further indicated that exogenous polyamines suppress the expression of TolA, BtuB, OmpF, and OmpC proteins that are responsible for ColE7 uptake. Moreover, two-dimensional gel electrophoresis revealed that the production of two periplasmic proteins, PotD and OppA, is increased in E. coli cells under ColE7 exposure. Based on these observations, we propose that endogenous polyamines may play a dual role in the ColE7 system. Polyamines may participate in initiating the expression of the SOS response of the ColE7 operon and simultaneously down-regulate proteins that are essential for colicin uptake, thus conferring a survival advantage on colicin-producing E. coli under stress conditions in the natural environment.

MAY 12, 2006•VOLUME 281•NUMBER 19 JOURNAL OF BIOLOGICAL CHEMISTRY 13083