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Journal of Bacteriology, April 1999, p. 2236-2243, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

A Conserved Domain in Escherichia coli Lon Protease Is Involved in Substrate Discriminator Activity

Wolfgang Ebel, Monica M. Skinner, Karen P. Dierksen, Janelle M. Scott, and Janine E. Trempy*

Department of Microbiology, Oregon State University, Corvallis, Oregon 97331-3804

Received 2 September 1998/Accepted 25 January 1999

Lon protease of Escherichia coli regulates a diverse set of physiological responses including cell division, capsule production, plasmid stability, and phage replication. Little is known about the mechanism of substrate recognition by Lon. To examine the interaction of Lon with two of its substrates, RcsA and SulA, we generated point mutations in lon which affected its substrate specificity. The most informative lon mutant overproduced capsular polysaccharide (RcsA stabilized) yet was resistant to DNA-damaging agents (SulA degraded). Immunoblots revealed that RcsA protein persisted in this mutant whereas SulA protein was rapidly degraded. The mutant contains a single-base change within lon leading to a single amino acid change of glutamate 240 to lysine. E240 is conserved among all Lon isolates and resides in a charged domain that has a high probability of adopting a coiled-coil conformation. This conformation, implicated in mediating protein-protein interactions, appears to confer substrate discriminator activity on Lon. We propose a model suggesting that this coiled-coil domain represents the discriminator site of Lon.

* Corresponding author. Mailing address: Department of Microbiology, Oregon State University, Nash Hall 220, Corvallis, OR 97331-3804. Phone: (541) 737-4441. Fax: (541) 737-0496. E-mail: trempyj{at}bcc.orst.edu.

Journal of Bacteriology, April 1999, p. 2236-2243, Vol. 181, No. 7
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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