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Journal of Bacteriology, August 1999, p. 4476-4484, Vol. 181, No. 15
Laboratoire d'Ingénierie des
Systèmes Macromoléculaires, Institut de Biologie
Structurale et Microbiologie, Centre National de la Recherche
Scientifique, 13402 Marseille Cedex 20, France
Received 1 March 1999/Accepted 18 May 1999
The Tol-PAL system of Escherichia coli is a
multiprotein system involved in maintaining the cell envelope integrity
and is necessary for the import of some colicins and phage DNA into the bacterium. It is organized into two complexes, one near the outer membrane between TolB and PAL and one in the cytoplasmic membrane between TolA, TolQ, and TolR. In the cytoplasmic membrane, all of the
Tol proteins have been shown to interact with each other. Cross-linking
experiments have shown that the TolA transmembrane domain interacts
with TolQ and TolR. Suppressor mutant analyses have localized the
TolQ-TolA interaction to the first transmembrane domain of TolQ and
have shown that the third transmembrane domain of TolQ interacts with
the transmembrane domain of TolR. To get insights on the composition of
the cytoplasmic membrane complex and its possible contacts with the
outer membrane complex, we focused our attention on TolR. Cross-linking
and immunoprecipitation experiments allowed the identification of Tol
proteins interacting with TolR. The interactions of TolR with TolA and
TolQ were confirmed, TolR was shown to dimerize, and the resulting
dimer was shown to interact with TolQ. Deletion mutants of TolR were
constructed, and they allowed us to determine the TolR domains involved
in each interaction. The TolR transmembrane domain was shown to be involved in the TolA-TolR and TolQ-TolR interactions, while TolR central and C-terminal domains appeared to be involved in TolR dimerization. The role of the TolR C-terminal domain in the TolA-TolR interaction and its association with the membranes was also
demonstrated. Furthermore, phenotypic studies clearly showed that the
three TolR domains (N terminal, central, and C terminal) and the level of TolR production are important for colicin A import and for the
maintenance of cell envelope integrity.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of TolR N-Terminal, Central, and C-Terminal
Domains in Dimerization and Interaction with TolA and TolQ
*
Corresponding author. Present address: Centre de
Biophysique Moléculaire, CNRS, UPR4301, University of
Orléans, rue Charles Sadron, 45071, Orleans Cedex 2, France.
Phone: 33 (0)2 38 25 55 67. Fax: 33 (0)2 38 63 15 17. E-mail:
benedett{at}cnrs-orleans.fr.
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