The Tol proteins of Escherichia coli and their involvement in the uptake of biomolecules and outer membrane stability

The Tol proteins of Escherichia coli are involved in outer membrane stabili ty. They are also required for the uptake of the group A colicins and the t ranslocation of filamentous phage DNA into the cytoplasm. The tol-pal genes constitute two operons in the E. coli genome, orf1tolQRA and tolBpalorf2. The TolQ TolR TolA proteins form a complex in the cytoplasmic membrane, whi le TolB and Pal interact near the outer membrane. Most of the amino acid re sidues of TolA, TolB, TolR and Pal are localized in the periplasm. Recent a dvances in the knowledge of interactions of Tol-Pal proteins with other env elope components, or with group A colicins, are presented, together with cu rrent hypotheses about the role of the Tol proteins in outer membrane stabi lity. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.