THE TON SYSTEM CAN FUNCTIONALLY REPLACE THE TOLB PROTEIN IN THE UPTAKE OF MUTATED COLICIN-U

The uptake of colicin U into sensitive cells is dependent on the Tol s ystem. Like colicin A and the E-type colicins, colicin U contains the consensus pentapeptide DG(T/S)G(S/W) in the N-terminal 36 amino acids, which have been proposed to be involved in the interaction of colicin U with the Tol proteins. The role of the DGTGW motif in colicin U was studied by converting it into the TonB box motif DTMVV of colicin B. Uptake of the mutated colicin U (DTMVV) depended on TonB and ExbB and still remained TolA- and TolQ-dependent, but no longer required TolB. The Ton system could obviously replace the TolB function in the uptake of the mutated colicin U. The colicin U derivative is the first colic in whose uptake depends on the Ton and the Tol systems. (C) 1998 Feder ation of European Microbiological Societies. Published by Elsevier Sci ence B.V. All rights reserved.